Many simple inequalities can be solved by adding, subtracting, multiplying or dividing both sides until you are left with the variable on its own.
But these things will change direction of the inequality:
Don't multiply or divide by a variable (unless you know it is always positive or always negative)
The second and the third ones
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
--------------
x=-9
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