Okay, let's tackle this math problem. We're starting with 73778 and subtracting 3780.

Step 1: We'll start by subtracting the digit 0 and the borrow 0 from 8 in column 1 and get 8.
8 is the first digit of our result.

Step 2: We'll start by subtracting the digit 8 and the borrow 0 from 7 in column 2 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

Step 3: We'll start by subtracting the digit 7 and the borrow 1 from 7 in column 3 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

Step 4: We'll start by subtracting the digit 3 and the borrow 1 from 3 in column 4 and get -1.
We add -1 to 10 and get 9 as the next digit of the result.

Step 5: We'll start by subtracting the digit 0 and the borrow 1 from 7 in column 5 and get 6.
6 is the next digit of our result.

So, 73778 - 3780 = 69998.