Write a function rule that gives the total cost c (p) of p pounds of sugar if each pound costs $0.42.

Since a pound of sugar increases proportionally to the total cost of sugar bought, then the function can be written as:

c (p) = 0.42p

Where: c (p) = total cost of sugar bought

p = pounds of sugar

c (p) is a function of p, because c (p) depends on p.