The division bar is a grouping symbol, equivalent to parentheses around both numerator and denominator. You must evaluate the numerator before you can divide by the denominator, which also must be evaluated before that division.
To find the cost per square foot of A you take $450/720ft to get $0.63 per foot and then for B oyu take $525/768ft to get $0.68 per foot so A is cheaper than B
