6x - 3y = 15.....multiply by 4
7x + 4y = 10....multiply by 3
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24x - 12y = 60 (result of multiplying by 4)
21x + 12y = 30 (result of multiplying by 3)
---------------add
45x = 90
x = 90/45
x = 2
6x - 3y = 15
6(2) - 3y = 15
12 - 3y = 15
-3y = 15 - 12
-3y = 3
y = -3/3
y = -1
solution is (2,-1) <==