Tan(x) = sin(x) / cos(x)
Csc(x) = 1/ sin(x)
You'll see this better if I use latex.

Now just cancel numerators with denominations. They all disappear. The cancelations leave 1 on both the numerator and denominator.
The diameter is 10 square inches
Its comparing least times, so 9.675 would be the winning time.why?you ask.well, change all the decimals to the thousandths(9.750,9.700,9.675). now you could see which is the least.
The answer is associative property because no matter how you group the numbers, you still get the same number. hopefully my answer helped you