Answer: 36.66m/s
Explanation:
Listing everything is gives you:
Vf = 0
a = -3.2
Δx = 210
Vi = ?
Pick one of the kinematic equations to find the missing variable
I used this one:
Δx
When you plug everything in, you get
0 =

add 1344 to both sides and square root to get Vi = 36.66