In this question , it is given that
A painter charges by the square foot and charges you $1,875 to paint a 750 square foot rental house.
For 750 square foot, he charges $1875.
So for 1 square foot, he charges
[tex] = \frac{1875}{750} = $2.50 \ \per \ square \ foot [/tex]
And for 1300 square foot, he charges
[tex] = 2.50*1300 = $3250 [/tex]