The era that dinosaurs came was in the Mesozoic Era!
The value of R3 is A) 10 Ω
I believe it is green at 1,550
Explanation:
Efficiency is defined as the ratio between the useful output over the total amount consumed. 
The fan does 500W of useful work while wasting 300 W. The total power consumption is 800 W (500 + 300).