At a restaurant the ratio of kids meal sold two adult males sold was 5 to 4 if there was 20 kids meal sold what is the combined amount of kids and adult meal sold

You would have 20 kids and 16 adults

First find out the total amount you need for your fabric.
2 1/2 yards for the shawl1 7/8 yards for the dress
The total would be    2 4/8  + 1 7/8  = 4 1/8 yards
Since you already have 9/10 of a yard, just subtract from your total amount.
  3  90/80  +  72/80 = 3 18/80 = 3 9/40   *good to simplify*
She needs 3 9/40 yards more of fabric.
You already have 9/10 of fabric so you don't need to pay for it.You need to just pay for the 3 9/40 yards.
3 * 6.87 = 20.61(6.87/ 40) * 9 = 1.54575 
20.61 + 1.54575 = 22.15575 *round it*
You need $22.16 to make the dance outfit.