Yes u r right 50 is the correct answer after u do all the required math. U can also figure it out by seeing that it only covers a 4 feet radius then u can pretty much just tell the answer of the asked question and hope u pass have a great day.
The answer would be C (P=T/2). This can be explained by examining the ratio. If you were to put in the answer of T = 12, then you would be looking for T/2 or 6, assuming we're giving them each half of the amount original held by grandmother.