Which expression is equivalent to StartFraction negative 18 a Superscript negative 2 Baseline b Superscript 5 Baseline Over Negative 12 a Superscript negative 4 Baseline b Superscript negative 6 Baseline EndFraction? Assume a not-equals 0, b not-equals 0. A. StartFraction 2 a squared b Superscript 11 Baseline Over 3 EndFraction
B. StartFraction 2 a squared b Superscript 30 Baseline Over 3 EndFraction
C. StartFraction 3 a squared b Superscript 11 Baseline Over 2 EndFraction
D. StartFraction 3 a squared b Superscript 30 Baseline Over 2 EndFraction

Naruto is choosing between two venues that will deliver food to his house. with probability 1/3 he will choose ramen mania (r), and with probability 2/3 he will choose sushi (s). if he chooses r, 15 minutes after making the call, the remaining time it takes the food to arrive is exponentially distributed with average 10 minutes. if he orders s, 10 minutes after making the call, the time it takes the food to arrive is exponentially distributed with an average of 12 minutes. given that he has already waited 25 minutes after calling, and the food has not arrived, what is the probability that he ordered from r? i am really stuck on how to set this up, so if you could be extra clear, that would be super ! in advance