If y varies directly as x, and y is 18 when x is 5, which expression can be used to find the value of y when x is 11?
rate of change

y = kx

Step-by-step explanation:

If y varies directly as x

That means y = kx

Where k is the constant of proportionality

If y = 18 and

x = 5

K= ?

Using y = kx

18 = k x 5

Divide both sides by 5

18/5 = k x 5 /5

3 3/5 = k

K = 3 3/5

Now , when x = 11

The expression to find y is

y = kx

Since k = 3 3/5 and

x = 11

y = 3 3/5 x 11

y = 18/5 x 11

Multiply through

y = 198/5

y = 39 3/5