Well, the way I would do this is count the course and write that first, than put the 2 colins and than the carton of milk ratio. I hope this helped!
Let X = pounds of Bermuda grass needed.
(20 pounds bahia grass x $6.30) + ( X x $3.65) = (20 +X) x $4.90
Simplify:
126 + 3.65X = 98 + 4.90X
Subtract 3.65X from each side:
126 = 98 + 1.25X
Subtract 98 from each side:
28 = 1.25X
Divide both sides by 1.25
X = 28 / 1.25
X = 22.4 pounds required.
12 cups I believe ! Hope this helps!