When Maggie applies the brakes of her car the car slows uniformly from 15.0 m/s to 0m/s in 2.5s

Remark

The usual question is either what is the deceleration or how far did she go before she stopped.

Equation

For Distance

d = (vf + vi) * t / 2

For Deceleration

a = (vf - vi) / t

Solution (Distance)

d = (vf + vi) * t/2

d = (15 + 0) * 2.5 / 2

d = 15 * 2.5 / 2

d = 37.5/2

d = 18.75

Solution Deceleration

a = (vf - vi) / t

a = (-15) / 2

a = - 7.5 m/s^2 It is minus because you are slowing down, not speeding up.