Question

if 4x+3y=21, 3x+4y=21 Then x+y=?​

Answer 1

Answer:

x+y=9

Step-by-step explanation:

4x3=12 21-12=9

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Answer 2

Answer:

x+y=6

Step-by-step explanation:

4x+3y=21 --- eq 1

3x+4y=21 --- eq 2

Eliminating x by elimination method,

Multiplying eq 1 by 3 & eq 2 by 4

12x + 9y = 63

-(+)12x -(+) 16y = -(+)84

-7y = - 21

y= 3

4x+9 = 21

4x= 12

x=3

x+y=3+3 = 6