y = - 25
since x varies directly with y then we can express the relationship as
x = ky ← k is the constant of variation
to find k use the given condition y = - 10 when x = 4
k = [tex]\frac{x}{y}[/tex] = [tex]\frac{4}{-10}[/tex] = - [tex]\frac{2}{5}[/tex]
hence x = - [tex]\frac{2}{5}[/tex] y
when x = 10
10 = - [tex]\frac{2}{5}[/tex] y
multiply both sides by - 5 and divide both sides by 2 )
- 50 = 2y ⇒ y = - 25
