Sara offers the better price.
Sara: 3 cookies is 2.49 1 cookie is x. that means:
x · 3 = 2.49
x= 2.49 divided by 3 = 0.4
John : 7 cookies = 5.39 1 cookie = y That means:
y · 7 = 5.39
y = 5.39 divided by 7 = 0.707
Conclusion: Sara is cheaper than John.
Hope this helps!-Aparri :)