Answer:
y = 72
Explanation:
Given y varies jointly as x and z then the equation relating them is
y = kxz ← k is the constant of variation
To find k use the condition y = 12 when x = 4 and z = 3
12 = k × 4 × 3 = 12k ( divide both sides by 12 )
1 = k
y = xz ← equation of variation
When x = 9 and z = 8 , then
y = 9 × 8 = 72