Written in 2-point form, the equation of the line is
y = (y2-y1)/(x2-x1)·(x-x1) +y1
y = (3-(-5))/(-6-(-4))·(x-(-4)) + (-5)
y = 8/-2·(x +4) - 5
y = -4x -21
The value of b is -21.
Y = 40x +15 because it charges 15$ as it's initial service fee and it charges an additional $40 a month so you multiply 40 times the number of months and add 15 to get the total after x amount of months
73-(10+3)=60 you have to add 7 and 3 first, then you subtract it from 73