Ashley bought mirrors for $80 for home furnishing store. she plans to sell them for $120. what is the percent markup based on cost

And explain how you got it so i can understand future problems : 3

65 8 7 4 5 6 8 4 3 2 1 9 5 6 4 2 1 6 5 1 5 1 3 2 3 5 multiply the third number in the first row by the seventh number in the third row. add this result to the fifth number in the second row. add to this total ten times the fourth number in the third row. subtract the eighth number in the first row from the result.

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10