You applied the rule improperly. When dividing exponents, you subtract the exponent of the denominator <em>from</em> the exponent of the numerator, not the other way around. The exponent you should have gotten was 
Just so you know, there's no diagram
5% = 0.5
0.5n = 85
Divide by 0.5
0.5n = 85
/0.5 /0.5
n = 170.
The number is 170.
8:20 pm because if Prisha read 60 pages for a half hour, and she read 40 until 8:40, it would be 8:20 pm