Arithmetic sequences
the richard family wants to build a human pyramid when they go to the beach this summer. they will put one person on top and add 2 more people for each descending row.

a. how many people will be in the seventh row?

b. find the total number of people in a pyramid with seven rows

c. next summer, sarah richard wants to build a pyramid with only the great-grandchildren. if they build it the same way. how many children are needed to make with 10 rows?