Answer:
y = - 140
Step-by-step explanation:
Given that 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 = - 180 when z = 15 and x = - 3, thus
- 180 = k × - 3 × 15 = - 45k ( divide both sides by - 45 )
4 = k
y = 4xz ← equation of variation
When x = 7 and z = - 5, then
y = 4 × 7 × - 5 = - 140
