These are quick questions because I've done them all I just dont know one part!

Q1: I don't know what part B is

The average cost per item, C, in dollars, of manufacturing a quantity q of cell phones is given by C = % + b , where a and b are positive constants. (a) Find the rate of change of the average cost per item as the quantity of cell phones increases. Use lower case letters. - V dollars percellphone :i (b) If production of cell phones increases at a rate of 60 cell phones per week, how fast is the average cost per item changing? Ex x 15 the average cost per item increasing or decreasing? increasing a decreasing v (a) Consider a rectangle of length L inches and width W inches. Find a formula for the perimeter of the rectangle. Use upper case letters. P= 2L+2W (b) If the length and width of the rectangle are changing with respect to time, nd % . Use % and % and not L' and W'. i = 2 (ii + 2 d_W V dt dt dt (c) Suppose the length is increasing at 4 inches per hour and the width is decreasing at 3 inches per hour. How fast is the perimeter of the rectangle changing when the length is 40 inches and the width is 100 inches? in/hr