C is the answer radical 77/22
18 more than 6 in a mathematical expression will be 18 + 6 or 6 + 18. Because we are adding 6 to 18 or 18 to 6.
Given:

He does mistake in the order of giving preference.
We should give preference in the order, division, multiplication, addition, subtraction.
But, he gave the first preferrence to the subtraction.
72-8=64
Next, he used division
64/2=32
Next he adds 32 with 8.
So, he gets 50.
But the actual simplification is,
Simplifying we get,

Hence, the correct value of the expression is 86.
The slope of the line is -3/4
-x+3x=2x
2x=2+6
2x=8
8/2=4
x=4