Hello from MrBillDoesMath!
Answer: y = 120
Discussion:
"y varies jointly as x and z" ==> y = k*x*z where k is a constant
Substitute y = 70, x = 7, z = 2 in this equation to determine the value of k
y = k *x * z
70 = k * 7 * 2 or
70 = 14k or
k = 5.
So y = 5 *x * z is the equation of variation.
Substituting x = 6 and z =4 in the equation gives
y = 5 * x * z = 5 * 6 * 4 = 120
Thank you,
MrB
