A set costs half as much as a book.A book costs 600$ more than a pen.If the total cost of the three items is 6900$,find the cost of a set.
B = 2S
B - 600 = P
B + P + S = 6900
2S + (B-600) + S = 6900
2S + (2S-600) +S = 6900
Solve for S.
B - 600 = P
B + P + S = 6900
2S + (B-600) + S = 6900
2S + (2S-600) +S = 6900
Solve for S.