6. The cost to mail a package is $5.00. Noah has postcard stamps that are worth $0.34
each and first-class stamps that are worth $0.49 each.
a. Write an equation that relates the number of postcard stamps p, the number of
first-class stamps f, and the cost of mailing the package.
b. Solve the equation for f.
c. Solve the equation for p.
d. If Noah puts 7 first-class stamps on the package, how many postcard stamps
will he need?