7. A function machine does the four operations shown in order.

Iris inputs a positive integer and the output is also a positive integer.
What is the smallest possible number which Iris could have input?
A 9
B 84
C 102
D 120
E 129
7. E Let the output from the function machine be $n$. Then the input is $((n+10) \times 3+10) \times 3=3(3 n+30+10)=9 n+120$. The smallest positive integer input occurs when $n=1$. Therefore the smallest possible positive integer which Iris could have input so that the output is also a positive integer is $9 \times 1+120=129$.