Solve. 3
b=-a
4
a + b = 21
a = 375
a = 20
b = 11
a = 12
b = 9
a = 20
b = 15
b = -16
167

b=9,a=12

Step-by-step explanation:

I solved by substitution:

b = 3/4a  ---> plug this into the other equation

a + b = 21   is now    a + 3/4a = 21

Reduce: 7/4a = 21

a = 12

Now solve for b:

b=3/4a is now b=3/4(12)

b=9

b

step-by-step explanation:

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