Firstly, you should aim to eliminate one of the unknown values. As b is positive and negative in each equation, this would be a good value to eliminate. Both equations would have to be multiplied to cancel out one of the values. For example, if equation 1 is multiplied by 2 and eqution 2 is multiplied by 5 you get:
Equation 1: 4a-10b= 22 Equation 2: 15a+ 10b= 35
Then add the two new equations together to cancel out b and simplify, which leaves you with:
19a= 57 therefore a= 3
Then substitute a with 3 in equation 1 or 2 to find out the value of b. For example, if substituted into equation 1 you get:
(2 x 3) -5b=11 therefore b=-1