The old budget was $75 because 15 x 5 = <<15*5=75>>75
They are adding $15 to the budget because 75 x .2 = <<75*.2=15>>15
The new budget is $90 because 75 + 15 = <<75+15=90>>90
They can buy 10 softballs on the new budget because 90 / 9 = <<90/9=10>>10
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