If y varies jointly as x and z, and y = 60 when x = 10 and z = –3, find y when x = 8 and z = 15.?

im pretty sure your final answer will be y=-240. this is how you get it: the formula for joint variation is y=kxz. y=60, x=10, and z=-3. plug this in and you get 60=k(10)(-3). You then simplify the right side to get 60=k(-30). Simplify further and you find that k=-2. Now you take the joint variation formula y=kxz and plug in x=8, z=15, and k=-2. Now you have y=(-2)(8)(15). multiply this out and you get -240.