Acceleration in mi/hr^

You need to be careful with units here.  The first question asks for the answer in miles/hr²; the answer is given in m/s².

The second example finds the difference in speeds given in miles/hr and divides by seconds, so the value given has units of miles/(hr.sec).

acceleration is change in velocity divided by time.  In 10 seconds the change in velocity is 26.82-17.88=8.94

then we divide by time, 10, to get .894m/s^2

thanks! whats the formula for deceleration? i have driving at 25mi/hr slam on breaks, and in 3 seconds speed decreases to 8mi/hr.

deceleration and acceleration are exactly the same thing!  The only difference is that if you lose speed your resulting acceleration will be negative.  In your example

(8-25)/3=-17/3

Much appreciated! 

This is AVERAGE acceleration of course.

Yes, I didn't notice that thank you Alan.