Question 165993
You are correct. The answer is {{{t=P/(Ir)}}}. If you aren't sure, try plugging in some numbers. For instance, let {{{I=2}}}, {{{r=10}}} and {{{t=5}}}. So 


{{{P=2*10*5}}} ----> {{{P=100}}}


Now let's say that {{{P=100}}}, {{{I=2}}} and {{{r=10}}} but now we do NOT know the value of "t". So this means that 


{{{100=2*10*t}}} ----> {{{t=100/(2*10)}}} ----> {{{t=100/20}}} ----> {{{t=5}}} (which was the original value we gave to "t")



This isn't a foolproof way to confirm your answer, but it may help you see what's happening.