Whats the difference between -5x + 7 and 3x - 2

How do you use the elimination method for this question? explain, because i really want to understand!

Δabc is dilated by a scale factor of 3 with the origin as the center of dilation to form δa′b′c′. the slope of is -1.2. the length of is p units, the length of is q units, and the length of is r units. the slope of is . the length of is units.

Select the correct answer and solve for y