y varies jointly as X and Z. y=64 when x=4 and z=8. Find y when x=8 and z=6

Answer 1

y = k ∙ x ∙ z

When x = 4 , y = 64 and z = 8:

y = k ∙ x ∙ z

64 = k ∙ 4 ∙ 8

64 = 32 k

Divide both sides by 32

64 / 32 = k

2 = k

k = 2

When x = 8 and z = 6:

y = k ∙ x ∙ z

y = 2 ∙ x ∙ z

y = 2 ∙ 8 ∙ 6

y = 2 ∙ 48

y = 96

Answer 2

y = kxz
so, y/(xz) = k, a constant

You want y such that

y/(8*6) = 64/(4*8)
y/48 = 2
y = 96