I do not know how to show working out mathematically for the question below to my 11 year old daughter.

In my greenhouse, a tomaoto plant anda sunflower plant are grown by side by side. On ath 24th June , the tomato plant is 16 cm tall whereas the sunflower is onlty 7 cms tall. The tomaoto plant grows at a constant rate of 1 cm per day and the sunflower plaqnt grows at a constant rate of 1.5 cm per day. On what day will the two plants have the same height?

Thanks

Dee