8th grade math problem involving pizzas and some kind of algebra

I have a problem where there are 3 people making 3 different kinds of pizza. it shows me how many pizzas were made by each person for each of 5 hours. Cheese: 6, 12, 8, 16, 12 Pepperoni: 5, 2, 7, 4, 9 and Veggie: 2, 8, 4, 16, 8. Then it goes directly to: the last hour(hour 10) 210 pizzas were made for each type of pizza. how many were cheese, veggie, pepperoni?

I actually found the answer but have no idea how they got the answer. Can anyone help?

Thanks!