Question 252923
hourly wages+commission=income
15*6.25+rate*sales=280.63
rate=r
sales=3250
15*6.25+r*3250=280.63
solve for r

I leave the math for you.
Be careful of decimal points
Make sure the results are reasonable.
He earned only about 90 dollars hourly wages so his commission  should be less than $200
So his r should probably be less than 7%
You do the exact calculations.