Ahat salesman earns a commission of 30% of all hat sales made. yesterday he sold 3 hats for $90 each and 4 hats for $50 each. how much did he earn in commission yesterday?

Percentage of commission earned by the hat salesman = 30 percent.
Amount of money for which 3 hats were sold = 90 * 3
                                                                        = 270 dollar
Amount of money for which 4 hats were sold = 50 * 4
                                                                        = 200 dollars
Then
Total amount of money for which 7 hats were sold = 200 + 270
                                                                                = 470 dollars
Amount of commission earned by the hat salesman = 470 * (30/100)
                                                                                   = 141 dollars
From the above deduction, the amount of commission earned by the hat salesman was $141. 

You can find the area of a rectangle by multiplying the length and height. so multiply 1/2*7/4(which is the simpler version of 1 3/4) and you get 7/8 as your answer.