Question 1190081
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Solve the first equation for y
x+y = 30
y = 30-x


Then plug this into the second equation
3x+4y = 100
3x+4( y )= 100
3x+4( 30-x )= 100


At this point we solve for x
3x+4( 30-x )= 100
3x+120-4x= 100
-x+120= 100
-x= 100-120
-x = -20
x = 20


Use this to find y
y = 30-x
y = 30-20
y = 10


Summary:
x = 20 and y = 10
The two lines cross at (20,10).
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