The equation is "V2=V1+at", where V2(final velocity)=45miles/hr, V1(initial velocity)=15 miles/hr, a=acceleration , and t(time)= 15 seconds. First we convert 15 secs to hours,.. It would be "1/240 hr",this will be the value of t.. Then we substitute all values in the equation to find the acceleration,.... V2=V1+at...45=15+a(1/240)...30=a(1/240)...a=7200... So The answer is 7200 Miles/hour. .. If you want it in meter/sec, the answer would be 3218.688 meters/sec.