18. Brian chooses an integer, multiplies it by 4 then subtracts 30 . He then multiplies his answer by 2 and finally subtracts 10 . His answer is a two-digit number. What is the largest integer he could choose?
A 10
B 15
C 18
D 20
E 21
18. E Let the integer Brian chooses be $x$. Following the operations in the question, his final result is $2(4 x-30)-10$. His answer is a two-digit number so $9<2(4 x-30)-10<100$. Hence we have $9<8 x-70<100$ which has solution $9 \frac{7}{8}<x<21 \frac{1}{4}$. Therefore the largest integer Brian could choose is 21 .