Solution: Suppose that red now has X pieces and light blue now has 4x pieces.

(x+ 18)÷(4x- 18)=4

x+ 18=4×(4x- 18)

x+ 18= 16x-72

16x-x= 18+72

15x=90

x=90÷ 15

x=6

Light light blue now has 4x = 4x6 = 24 pieces.