Juca has decided to call all positive integers with 8 digits as $sextalternados$ if it is a multiple of 30 and its consecutive digits have different parity. At the same time, Carlos decided to classify all $sextalternados$ that are multiples of 12 as $super sextalternados$.

a) Show that $super sextalternados$ numbers don't exist.

b) Find the smallest $sextalternado$ number.
### Part (a)
To show that $super\ sextalternados$ numbers don't exist, we need to prove that no 8-digit number can satisfy all the conditions of being a $super\ sextalternado$.

1. **Divisibility by 30**:
   - A number divisible by 30 must be divisible by both 3 and 10.
   - For divisibility by 10, the last digit must be 0.
   - For divisibility by 3, the sum of the digits must be divisible by 3.

2. **Divisibility by 12**:
   - A number divisible by 12 must be divisible by both 3 and 4.
   - We already have the condition for divisibility by 3.
   - For divisibility by 4, the last two digits must form a number divisible by 4.

3. **Alternating parity**:
   - Consecutive digits must have different parity (one even, one odd).

Given these conditions, let's analyze the last two digits of a $super\ sextalternado$ number:
- The last digit is 0 (since it must be divisible by 10).
- The second last digit must be odd (to maintain alternating parity).

Thus, the last two digits can be 10, 30, 50, 70, or 90. However, none of these pairs are divisible by 4. Therefore, no 8-digit number can satisfy all the conditions of being a $super\ sextalternado$.

\[
\boxed{\text{None}}
\]

### Part (b)
To find the smallest $sextalternado$ number, we need to find the smallest 8-digit number that is a multiple of 30 and has alternating parity.

1. **Constructing the number**:
   - The number must end in 0 (to be divisible by 10).
   - The second last digit must be odd (to maintain alternating parity).

2. **Checking the smallest candidate**:
   - Start with the smallest possible digits and alternate parity: 10101030.
   - Check if it is divisible by 3:
     \[
     1 + 0 + 1 + 0 + 1 + 0 + 3 + 0 = 6 \quad (\text{which is divisible by 3})
     \]
   - Check if it is divisible by 30:
     \[
     \text{It ends in 0 and is divisible by 3, so it is divisible by 30.}
     \]

Thus, 10101030 is a valid $sextalternado$ number. To confirm it is the smallest, consider any smaller number of the form 101010a0:
- If $a = 1$, the number is 10101010, but:
  \[
  1 + 0 + 1 + 0 + 1 + 0 + 1 + 0 = 4 \quad (\text{which is not divisible by 3})
  \]

Therefore, 10101030 is indeed the smallest $sextalternado$ number.

\[
\boxed{10101030}
\]