To convert the temperature of mass #m# from #theta_1# to #theta_2#,having a specific heat of #s#,heat energy(#H#) required is given as, #H= ms (theta_2 - theta_1)#
Here, #m=50 gm , (theta_2 - theta_1) =(50-25)=25,s=1# CGS unit for water)
So, #H = 50*1*25 = 1250 # calories