How do i get r alone on one side of the equation; 15 = 2(3.14)r

Water flows at a steady rate from a tap. its takes 40 seconds to fill a 4 litre watering can from the tap. the rate at which water flows from the tap is halved. complete: 4 litres into cm3

Wrote and expression for the difference of p and 4

In which direction does the left side of the graph of this function point? f(x) = 3x3 - x2 + 4x - 2