Aviolin was on sale of 50% off. the sale price
is $50. what was the original price?

Let us assume the original price of the violin to be = x
Sale price of the violin after discount = $50
Percentage of discount given on the violin = 50%
The
(50/100) * x = 50
x/2 = 50
x = 50 * 2 dollars
   = 100 dollars
So the original price of the violin was $100. I hope the procedure is clear enough for you to understand. You can always use this procedure for solving similar problems without the necessity of taking any external help.

1.17+3.99a. you combine the terms with a to create 3.99 and the 1.17 stays because it has no like terms or a variable