Question 1095574
<font color="black" face="times" size="3">x = number of programs that Hans bought
profit per program = selling price - purchase price
profit per program = 3.00 - 1.50
profit per program = 1.50 dollars
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If Hans sold all x programs, then he would make a profit of 1.50*x dollars; however, he "sold all but 20 of them" meaning that he actually sold x-20 programs. He sold them at a profit of 1.50 dollars per program


The total profit expression is 
1.50*(x-20)
1.50*x + 1.50*(-20)
1.50x-30


This expression is then set equal to 15 (because the given total profit is $15). Now solve for x


1.50x-30 = 15
1.50x-30+30 = 15+30
1.50x = 45
1.50x/1.50 = 45/1.50
x = 30


So <font color=red>Hans bought 30 programs</font> (he was able to sell 10 of them; 10*1.50 = 15 dollars total profit)</font>