It is given Hannah received $30 for her birthday and bought 3 shirts that were all the same price.
Let us suppose price of each shirt is $x
Hannah bought 3 shirts of equal value.
Cost of 3 shirts = $3x
Total amount received by Hannah is $30
After buying three shirts Hannah is left with $9
Cost of shirts + amount left = Total amount
3x+9=30
Option D.3x + 9 = 30 is the right answer.