How many litres were milked from each cow each year?

Question

The first year, two cows produced 8100 litres of milk.The second year their production increased by 15% and 10% respectively,  and the total amount of milk increased to 9100 litres a year.  How many litres were milked from each cow each year? 

Answer 1

x + y = 8100

x + x * 0.15 + y + y * 0.10 = 9100

Rewrite the second equation by combining like terms. Then either use elimination or substitution to solve for the variables.