I assume that this is a system of equations so I'll use the substitution method.
Make one of the equations equal an isolated variable and since x is already isolated just add -3y on both sides.
x-3y=-24
+3y +3y
x=3y-24
Substitute that in for the first equation.
2(3y-24)+9y=27
6y-48+9y=27
15y-48=27
+48 +48
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15y=75
----- ----
15 15
y=5
Substitute y in the other equation and find x
x-3(5)=-24
x-15=-24
+15 +15
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x=-9