Answer
The speed is 5.7 m/s just as the light turns green.
Work Step by Step
The car moves 20 meters in 1.0 second. Then the car needs to travel 180 meters in 14 seconds. We can find the speed after slowing for 14 seconds as:
$v_{ave}~t=x$
$\frac{v+v_0}{2}~t = x$
$v = \frac{2x}{t}-v_0$
$v = \frac{(2)(180~m)}{14~s}-20~m/s$
$v = 5.7~m/s$
The speed is 5.7 m/s just as the light turns green.
