Given :
if you buy 7 of them it will only cost you 2.80
let the cost of one cookie = x
so, the equation will be :
[tex]7x=2.8[/tex]So, the cost of one cookie on sale = x = 2.8/7 = 0.4
But, the cost on sale is 0.75 less than normal price
so, the normal price will be = y
so,
[tex]\begin{gathered} y-0.75=0.4 \\ y=0.4+0.75=1.15 \end{gathered}[/tex]So, the cost of one cookie = 1.15