If we take b to be bagels and m to be muffins, then it is clear that this is a system of equations. You hvae two equations and 2 variables that are unknown.
"a bagel and three muffins for $7.25." translates to b + 3m = 7.25 (equation 1)
"bagel and 2 muffins for $6" translates to b + 2m = 6 (equation 2)
We can solve for b (we could have solved for m as I will explain later) in the second equation.
b = 6-2m (equation 3)
We can now put equation 3 into equation on replace the b there. We will call this equation 4.
(6-2m)+3m = 7.25 (equation 4)
We can now solve equation four for m.
m = 1.25
Each muffin costs 1.25. We can now plug the costs of muffins back into equation 3.
b = 3.5
Each bagel is 3.50.
You could have solved for m initially and would have done this with the other equation. (solve for m and plug into the other equation) I will leave that as an exercise, but you will get the same results if you do it correctly.