What is the first step to finding he value of x in the equation

The number of revolutions of two pulleys is inversely proportional to their diameters. if a 24-inch diameter pulley making 400 revolutions per minute is belted to an 8-inch diameter pulley, find the number of revolutions per minute of the smaller pulley.

What are the solutions to the equation 4x2+3x=24-x

If y varies directly as x2 and y=6 when x=6, find the constant of variation.