A projectile initially at rest is vertically launched from the ground level. It is known that the projectile has first accelerated upward for 2.0 s with a constant acceleration of 5.0 m/s^2 and then decelerated with a constant rate of 10 m/s^2 until it reaches its highest possible point along the vertical direction. Determine the highest altitude the projectile reaches above the ground level.

a. 15 m
b. 8.0 m
c. 5.0 m
d. 12 m
e. 2.0 m
f. 10.0 m