We calculate acceleration with the formula, a= \frac{v-u}{t} . So subsitute the values in the formula, so it's  \frac{72-54}{15} . We need to multiply it by  \frac{60}{1} because the speed is 15 second and we need to convert it to hour. 72-54 is 18 and multiplied by 60 is 1080. Then divide it by 15 which is 72 km/hr. Your answer will be 72 km/hr :).

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Thank you so much
The si unit of acceleration is m/s. Then howcome 72. I got 1/3
I didn't do it according to the acceleration, please report my answer then.
Sryyyy 1/50