The sum of two numbers is 159 ,while the difference of the two numbers is 21. What are the two numbers?

Question

 The sum of two numbers is 159 ,while the difference of the two numbers is 21. What are the two numbers?

Answer 1

x+y=159

x-y=21

 

solve one equation for x

x=y+21

 

substitute

y+21+y=159

2y=138

y=69

 

x+69=159

x=90