We don't know how many of each flower that he bought, so we can use variables to represent each. Let x represent the number of roses, and y represent the number of daisies. Since he bought a total of 15 flowers, then:
x + y = 15
We also can express the total amount spent algebraically, since we know the cost of each type of flower.
3x + 0.75y = 24.75
We now have a system of linear equations. It would probably be easiest to solve this system by substitution. For example, we can solve the first equation for either x or y, and then substitute this into the second equation. You should be able to proceed from here.
