An easier question all wrong or or no-work answers will be reported.

3x-9y+3
6x-3y=-24

solve using two different methods(substitution/elimination) and explain which method you found to be more efficient.

Elimination: 

3x - 9y = 3
6x - 3y = -24

3x - 9y = 3
18x - 9y = -72
(subtract)
-15x = 75
÷ -15
x = -5

(3 × -5) - 9y = 3
-15 - 9y = 3
+ 15
-9y = 18
÷ -9
y = -2

Substitution:

6x - 3y = -24
+ 3y
6x = -24 + 3y

÷ 6
x = 4 + 0.5y

3(4 + 0.5y) - 9y = 3
12 + 1.5y - 9y = 3
12 - 7.5y = 3
- 12
-7.5y = -9
÷ -7.5
y = 1.2

x = 4 + (0.5 × 1.2)
x = 4 + 0.6
x = 4.6

So this one didn't fail as much, but I got different numbers. If you have to give in values, I'd give in the values from the elimination because I don't trust myself when it comes to the substitution