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Help me please..

Suppose a car is moving in a straight line and steadily increases its
speed. It goes from 0 miles/hour to 15 miles/hour the first second and 15
miles/hour to 30 miles/hour the next second. What is the acceleration?

A)10 miles/hour/second

B) 15 miles/hour/second

C) 20 miles/hour/second

D)30 miles/hour/second