Answer:
z = 189/44
Step-by-step explanation:
The "varies jointly" relationship can be expressed by ...
y = kxz
We can find k from the given values.
40 = k(10)(9)
40/90 = k = 4/9 . . . divide by the coefficient of k
Now we want to find z for given values of x and y. That can be found from ...
y = (4/9)xz
9y/(4x) = z . . . . . multiply by 9/(4x)
Filling in the new numbers, we have ...
z = 9·105/(4·55)
z = 4 13/44 = 189/44 ≈ 4.2954...(repeating 54)
