Final answer:
The correct answer is that z varies jointly as x and y with the formula z = xy/2, obtained by establishing the joint variation relationship and using the given values to find the constant of variation.
Step-by-step explanation:
The question asks us to determine how z varies jointly as x and y in a mathematical relationship. Given that z = 60 when x = 5 and y = 6, we can establish a proportional relationship where z is directly proportional to the product of x and y. Therefore, we can write the equation as z = kxy, where k is the constant of variation. To find the value of k, we use the given conditions: 60 = k(5)(6), which simplifies to k = 2. Hence, the general equation for z is z = 2xy, and the correct answer is d. Z = xy/2.