Could someone please help me with these problems:

1. The rate of sales of a new cell phone is given by the twice-differentiable function C, where C(t) is measured in thousands of units per month and t is measured in months from the cell phone's release date. The cell phone company recorded these sales data:

t (months)	0	3	4	5	8	10
C(t) (thousands of units/month)	80	75	65	30	20	10

Part A: Use a left Riemann sum with five subintervals indicated by the data in the table to approximate