How many 2-digit numbers are not divisible by 13

Это на английском? напиши на русском я вроде в математике разбираюсь!

Two-digit numbers start from 10 and go up to 99, so there's 89 two-digit numbers.
if you'd try to figure out how many of them ARE divisible by 13, you'd get a 7.
so 89-7=82