substitution is a method, not a problem (though it appears to be a problem for you! :-)
taking the first equation, solve for x or y:
x = (16+3y)/2
now "substitute" that into the other equation
5(16+3y)/2 + 2y = 21
80+15y + 4y = 42
19y = -38
y = -2
so, x = (16-6)/2 = 5
check that (5,-2) fits both original equations, just to be sure
I need help solving these problems by using the substitution problem
2x-3y=16
5x+2y=21
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