One day a store sold 23 sweatshirts. White ones cost $9.95 and yellow ones cost $13.50. In all, $278.55 worth of sweatshirts were sold. How many of each color were sold?
w + y = 23
9.95 w + 13.5 y = 278.55
y = (23-w)
so
9.95 w + 13.5 (23-w) = 278.55
solve for w