a) Let b and r represent the cost of a bag of bark mulch and red mulch, respectively. (Always start with a "let" statement that defines your variables--usually based on what the question is asking: cost of each type.)
8b +6r = 44.50 . . . . Paul's first purchase
1b +8r = 25.50 . . . . .Paul's second purchase
b) There are many ways to solve a set of linear equations like this. I like a graphical calculator because it gives me the solution without having to think too much or do any arithmetic.
(b, r) = (3.50, 2.75)
Pine bark mulch costs $3.50 per bag.
Red mulch costs $2.75 per bag.
c) The project cost would have been
.. 14*$3.50 +10*$2.75 = $76.50
Paul would NOT have been able to make that purchase with funds available.