The graphs of 4x+12y=8 and y=mx+5 are perpendicular. What is the value of m?

What is the missing step in this proof ?

The art class is planning to paint a mural on an outside wall. this figure is a scale drawing of the wall. width: 11 in length: 28 in unit rate: 1.5 ft per in. write the ratio of the area of the drawing to the area of the actual mural. write your answer as a unit rate. show that this unit rate is equal to the square of the unit rate 1.5 ft per in

Lola says these two expressions have the same value. expression a expression b which explains whether lola is correct?