Question

z varies jointly as x and y and inversely as w. Write the appropriate combined-variation equation, and find z for the given values of x, y and w. z = 10 when x = 5, y = -2 and w = 3; x = 8, y = 6 and w = -12

Answer 1

hm. I hope I'm interpreting this correctly but

z is jointly (directly) related with x and y so we have something like

z = kxy for a constant k

inversely with w implies the w is in the denominator

making z = kxy/w the combined equation

Answer 2

then you would plug in z = 10 when x = 5, y = -2 and w = 3 to solve for k

and after that you would use the other set of values x = 8, y = 6 and w = -12 to solve for z