5. In a two-digit number, the number of tens is two times less than the number of units. If you subtract the sum of its digits from this two-digit number, you get 18. Find this number.
5. According to the condition, in a two-digit number, the number of tens is twice less than the number of units, i.e., the number of units is twice the number of tens.

Two-digit numbers that satisfy this condition:

$$
12 ; \quad 24 ; \quad 36 ; \quad 48 .
$$

The sum of the digits of each of the obtained numbers:

$$
1+2=3 ; \quad 2+4=6 ; \quad 3+6=9 ; \quad 4+8=12
$$

Subtract the sum of the digits from the given numbers.

$$
12-3=9 ; \quad 24-6=18 ; \quad 36-9=27 ; \quad 48-12=36
$$

Thus, the number that satisfies the condition of the problem is 24.

Answer: 24.