Call the pencils x, the crayons y.
4x + 3y = 20.7 inches -> 16x + 12y = 82.8 inches.
5x + 4y = 26.4 inches -> 15x + 12y = 79.2 inches.
We minus the top one from the bottom -> x = 82.8 - 79.2 = 3.6 inches
Replace back : 4 x 3.6 + 3y = 20.7
14.4 + 3y = 20.7
3y = 6.3
y = 2.1
So, the length of 1 pencil is 3.6 inches, the length of 1 crayon is 2.1 inches
Recheck : 4 pencils and 3 crayons = 3.6 x 4 + 2.1 x 3 = 14.4 + 6.3 = 20.7
5 pencils and 4 crayons = 3.6 x 5 + 2.1 x 4 = 18 + 8.4 = 26.4
