2 dimensional motion - calculate magnitude of acceleration

[new^2^physics]

Homework Statement

an automobile manufacturer claims that its product will, starting from rest, travel 0.40 km in 9.0s. What is the magnitude of the constant acceleration required to do this?

2. The attempt at a solution

Vi = 0 m/s
t = 9.0 s
xi = 0 m
xf = 400 m

xf- xi = Vit + 1/2At²
1/2 A = xf-xi-Vit/t²

400m - 0 - (0)(9)/(9²) = 1/2A

a = 9.88 m/s²

POSSIBLE ANSWERS:

a. 9.9 m/s2
b. 8.9 m/s2
c. 6.6 m/s2
d. 5.6 m/s2
e. 4.6 m/s2

My vote is for "a" IS THIS CORRECT? I find physics very difficult and would appreciate any guidance. Thank you very much!

 

[G01]

I agree, a is the answer.