We have to find b first:
3 = -3/2(10)+b
3 = -15+b
18 = b
Now right the equation, your slope will be the same one....
Y = -3/2x + 18
X = 15
X + 90 = 7x
X = 7x - 90
X - 7x = -90
-6x = 90
Divide both sides by -6
X = 15
-19m-19 = 4m-4m+19
-19m-19 = 0+19
-19m = 19+19
-19m = 38
m = 38÷(-19)
m = -2