Hi Everyone , I was confused as well but after reading your comments it become easy to understand
Average power ( Pmax+Pmin)/2
At T=0 , (25+25)/2 = 25
At T=15 , (50+25)/2 = 37.5
At T=30, (75+50)/2 = 62.5
At T=45 , (50+50)/2 = 50
For the max power , I will quote the best comment above...