Over a period of 9.0 seconds a plane changes its velocity from 29.5 m/s to 45.7 m/s. What is its uniform acceleration?

----------------
I'm reviewing for my final and i can not think of what the formula to solve this is.

Average acceleration

= (Change in velocity) / time
Assuming the direction of the plane has not changed, then
acceleration
= (45.7 - 29.5) m/s / 9 sec.
= ? m/s²