Question 760220
Hello, 
With this:
a + b = 23
7a + 5b = 5 
You almost had is set up correctly. The right way is:
a + b = 23
7a - 5b = 5
We can solve this two different ways; Substitution or elimination.Let's do substitution by setting the first equation as:
a=23-b and plug this into the second equation as:
7(23-b)-5b= 5
Now we have one variable (b) to solve:
161-7b-5b=5
Simplify and subtract 161 to get:
12b= -156
Divide by 12 and we get:
b=13
Now that we know what the value of b is we can plug this into the first or second equation to find the answer for "a". I'lllet you figure that one out. 
Make sense?
RJ
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