Just ask from another angle (unify the number of carrots)

Note: 2 radishes for 8 carrots (2×5= 10 radishes for 8×5=40 carrots).

And because: 10 radishes can be exchanged for five Chinese cabbages.

Five Chinese cabbages can be exchanged for 40 carrots.

40÷5=8 means 1 Chinese cabbage can be exchanged for 8 carrots (⊙ _ ⊙).

8×4=32 (roots) Four Chinese cabbages for 32 carrots.

-Mr. Da Dan is a guest O(∩_∩)O~