30 pens and 75 pencils were purchased for 690 . if the average price of a pencil was 2.00 , find the average price of a pen .
"since average price of a pencil = 2 ∴ price of 75 pencils = 150 ∴ price of 30 pens = ( 690 – 150 ) = 540 ∴ average price of a pen = 540 ⁄ 60 = 18 answer c"
divide(subtract(690, multiply(75, 2.00)), 30)