What is the variable in this expression, 4m+17?

Which of the following lines is not parallel to the graph of y = 4x +7?

What adds to be the bottom number but also multiplies to be the top number with 8 on the bottom and 15 on top

How many 3-digit numbers can you write using only digits 1 and 7? (of course, digits can repeat.) how many 3-digit numbers can you write using only digits 1 and 7? (of course, digits can repeat.)