If you have multiple equations with multiple variables, you can either do clever substitutions, or turn it into a matrix on which you can perform linear combinations or multiplications (Gauss elimination)
1 1 1 1
2 1 -1 8
1 -1 1 -5
(note how the above 3 rows represent the 3 equations, just got rid of the variables, plus sign and equals sign)
subtract row1 from row3, that eliminates x and z from row 3.
1 1 1 1
2 1 -1 8
0 -2 0 -6
divide row3 by -2, that will give y a factor of 1
1 1 1 1
2 1 -1 8
0 1 0 3
The last row now says y=3
Answer:
the probability of getting a number less than 7 when rolling a standard dice is 100%
Step-by-step explanation:
All you gotta do is multiply the cm by 15,
For 13) you'd do

14)
15)

then for 16)