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.