Hello,
to find the total cost (c) of the colored strips we have to multiply the number of strips (n) by the cost of each color strip (99¢), that as an algebraic function is:
\(\boxed{c= n*99}\) [¢]
Now, if we use 3 solid color strips, that means that we use 4 patterned strips, so:
\(Cost=3*0.99+4*1.25 \\ \boxed{Cost= 7.97}\)
Answer: c=n*99 and Cost per curtain= $7.97