Question 876476
{{{3j^2 + 17j + 8k - 84 = 0}}}
{{{-j + 8k - 63 = 0}}}
Subtract the 2nd equation from the first equation
{{{3j^2 + 17j + 8k - 84 = 0}}}
{{{ 0  - j +  8k   - 63 = 0}}}
---------------------------------subtraction eliminates k

3j^2 + 18j + 0 - 21 = 0
A quadratic we can factor
(3j - 3)(j + 7) = 0
3j = 3
j = 1
and
j = -7
:
Use the 2nd equation to find k
when j = 1
-1 + 8k - 63 = 0
8k = 63 + 1
k = 8, when j = 1
:
When j= -7
7 + 8k - 63 = 0
8k = 63 - 7
k = 56/8
k = 7 when j = -7
:
:
Check solutions in 1st equation
j=1, k=8
3(1^2) + 17(1) + 8(8) - 84 = 0
3 + 17 + 64 - 84 = 0
j=-7, k=7
3(-7^2) + 17(-7) + 8(7) - 84 = 0
147 - 119 + 56 - 84 = 0