4. Thomas is at a store buying school clothes. T-shirts are on sale for $13 each and jeans are on sale for $18 each.

a) Write an equation that represents the total cost for x T-shirts and y pairs of jeans.

I need help with a..

b) Thomas bought six T-shirts and his total bill came to $168. How many pairs of jeans did he buy? Show all your work.

$13 x 6 (T) = $78.00
$18 x 5 (J) = $90.00
$90.00 + $78.00 = $168.00

x and y are defined in the question, so the cost equation would be

cost = 13x + 18y

so for b) you know cost = 168, x = 6

168 = 13(6) + 18y
168 = 78 + 18y
90 = 18y
y = 90/18 = 5
He bought 6 t-shirts and 5 pairs of jeans