How would i solve this algebra 2 problem?

Question

6L + 20S = 270

4L + 25S = 285

8L + 16S = X

Answer 1

start with just the first two.

6L + 20S = 270

4L + 25S = 285

throw into a matrix and do rref on a graphing calculator.

| 6 20 270 |

| 4 25 285 |

gives you an answer of (15,9)

then plug into the third equation and solve for x

8(15)+16(9)=x

x=264

make it a good day

Answer 2

6L + 20S = 270 (solve by using substitution)

4L + 25S = 285

8L + 16S = X

4L + 25S = 285

4L = 285 - 25S

L = (285 - 25S)/4

6L = 6(285 - 25S)/4

6L + 20S = 270

6(285 - 25S)/4 + 20S = 270

3(285 - 25S)/2 + 20S = 270

2[(855 - 75S)/2 + 20S] = 2[270]

855 - 75S + 40S = 540

-75S + 40S = 540 - 855

-35S = -315

S = -315/-35

S = 9

4L + 25S = 285

4L + 25(9) = 285

4L + 135 = 285

4L = 285 - 135

4L = 150

L = 150/4

L = 75/2 (37.5)

8L + 16S = X

X = 8(75/2) + 16(9)

X = 300 + 144

X = 444

∴ L = 75/2 (37.5) , S = 9 , X = 444

Answer 3

In the first equation:

L=0

S=13.5

In the third equation:

X=216

Answer 4

12L + 40S = 540 (from equation 1)  ---- equation 3

12L + 75S = 855 (from equation 2)  ---- equation 4

equation 4 minus equation 3 gives:

35S = 315

S = 9

Then substitute S=9 into equation 1:

6L + 180 = 270

6L = 90

L=15

So now you know L and S so

8L + 16S = 120 + 144 = 264