Since the amount of juice sold is equal. The initial difference between the strawberry and pear juice is constant.

From there the difference between before and after the sales should be made constant/ find the LCM

So under such circumstances.

Strawberry (SB): Pear (P): Difference (D) before will be
9:5:4 X 3

SB: P: D After will be
5:2:3 X 4

The ratios will then become
SB (before): P (before): Difference (constant): SB (after): P (after)

27:15:12:20:8

If you realised both the SB and P lost the same amount of units, which is consistent with the fact that both sold 56L of juice.

Therefore since 7u = 56
1u=8

Strawberry Juice before therefore is 27u x 8
=216L