Two similar books and three identical pencil boxes cost $42. Two similar books and six identical pencil boxes cost $60. How much does each pencil box cost?
2b + 3p = 42
2b + 6p = 60
subtract them:
3p = 18
p = 6
sub into 2b + 3p = 42
2b + 18 = 42
2b = 24
b = 12
a book costs $12 and a pencil box costs $6