4 1 2 x 15 3 4 July 8, 2019 16 32 64 128 4 1 2 x 15 3 4 sandpaper 2 x 4 )/ 3 4 2x 1 )/ 15 Air filter 15 3 4 x 19 1 2 x 3 4 15 4 x 3 )= 1 3x 2 x 4 15 x 7 4 3 2 1 4 4 1/2 + 1 1/3 4 x - 15 = 1/2 4 + 4 = 12 4/15 x 3