The solution to the problem is as follows:
First, I'd convert 188 mi/hr to ft/s. You should end up with about ~275.7 ft/s.
So now write down all the values you know:
Vfinal = 275.7 ft/s
Vinitial = 0 ft/s
distance = 299ft
Now just plug in Vf, Vi and d to solve
Vf^2 = Vi^2 + 2 a d
BTW: That will give you the acceleration in ft/s^2. You can convert that to "g"s by dividing it by 32 since 1 g is 32 ft/s^2.