Answer:
a = - 4, b = 9
Step-by-step explanation:
The equation of a line in slope- intercept form is
y = mx + b ( m is the slope and b the y- intercept )
y = ax + b is in this form
with slope = a = - 4
y = - 4x + b ← is the partial equation of the line
To find b substitute (- 3, 21) into the partial equation
21 = 12 + b ⇒ b = 21 - 12 = 9
