Answer:
y = m x + b equation of straight line
3 = -12 m + b using (-12, 3)
Also y = 1.5 x - 4 is perpendicular to line 1 (rearranging terms)
so m' = 1.5 and m = -1 / 1.5 by definition of perpendicular lines
3 = -12 (-1 / 1.5) + b using m in the first equation
3 = 8 + b and b equals -5
Check: 3 = -12 (-1 / 1.5) - 5 is then our first equation
using (-12, 3)
3 = 8 - 5 = 3
