Given the task definition and input, reply with output. You are given a math word problem and you are supposed to apply a single mathematical operator like addition, subtraction, multiplication, or division on the numbers embedded in the text to answer the following question and then only report the final numerical answer.

there are 45 questions on the math test . 17 questions are word problems . 28 questions are addition and subtraction problems . steve can only answer 38 questions . what 's the difference between the number of all questions on the math test and the number of questions that steve can answer ?

7