Order of operations (from high priority to low priority):
Parentheses
Exponents
Multiplications/Division
Addition/Subtraction
All in left to right.
2 ÷ (5 + 3)⁻¹ ÷ 4
2 ÷ (8)⁻¹ ÷ 4
2 ÷ 1/8 ÷ 4
16 ÷ 4
= 4
6:42 pm bc subract 2 hours is 12:12am and then subtract the rest is 7:12pm then you subract 12 minutes is 7 pm the subtract the 18 minutes left is 6:42 pm
Since 
(density = mass/volume), we can get the mass/weight of the liquid by integrating the density 
over the interior of the tank. This is done with the integral
which is more readily computed in cylindrical coordinates as
F(-3) = 8
Plug -3 into x and just solve it.
The ratio 4 to 7. would be 12 and 21
