Before braking, you travel at 20 m per second for 0.7 seconds, making 14 m.
The remaining distance to the intersection is 110 - 14 = 96 m
Now use that equation of motion which includes
distance S, acceleration a and starting and end velocities, u and v.
v^2 - u^2 = 2aS
Final velocity v = 0
Start velocity u = 20
Distance S = 96
0 - (20^2) = 2 * a * 96
a = 25/12 ~ 2.0833 m/s^2
Hope that helps,
Regards - Ian
AOL Health