Question

A+b=77,a-b=13 care sun nr

Answer 1

It's a simultaneous equation:
Steps:
1.Number the equations..

a+b=77 -1
a-b=13 -2

2. Choose what variable you want to use. In this case I would use the "b". Since the signs in front of the "b's" are different, add the two equations together

a + b = 77
+ + +
a (-b) = 13

Which gives;
2a = 90

Then solve to find a:
2a=90
a= 90/2
a=45

3.Then plug the "a" value into any of the original equations to find the "b" value. I would use equation 1 since the all the variables are positive.

a + b = 77
(45) + b = 77
b=77-45
b=32

4.Solution

a=45
b=32