Olivia is working on the problem below. Substitute x = -4/9 and y into the expression 3y - 8x.

Olivia thinks the correct answer is 3(1/2) -8(1/2); however, she is incorrect. Find Olivia's mistake.

Correctly substitute x = -4/9 and y into the expression 3y - 8x.

Explain the steps you took to substitute the values into the expression.

this is a direct variation proportion. y = kx

y is the total amount due, k is the constant of variation, and x is the number of texts sent.

plug in the 3.20 and the 16 to solve for the "k". this is the constant of proportionality. it is the value that will not change.

3.20 = k(16). solving you get $.20 per text.

the equation would then be y = .20x