I need to know how to write a pair of linear equations in two variables from a word problem

Harry the Hungry Hippo is munching on the lily pads in his pond. When he got to the pond, there were 20 lily pads, but he is eating 4 lily pads an hour. Heinrick the Hungrier Hippo found a better pond with 29 lily pads! He eats 7 lily pads every hour.
- If Harry and Heinrick start eating at the same time, when will their ponds have the same number of lily pads remaining?
b. How many lily pads will be left in each hole at that time?