Answer: your answer is C. there is no common factor between 6 and 15.
Oi
Just calculating the differential. Step by step:

If you want to know where the tangent has no slope:
The best step to do next is to add 80 to both sides of equation:
5 ( x² + 8 x ) + 80 = 14 + 80
and since 80 = 5 · 16
5 ( x² + 8 x + 16 ) = 94 Answer : B )
After that we will continue like this:
5 ( x + 4 )² = 94
( x + 4 )² = 18.8 ... etc
Answer:
, 
Step-by-step explanation:

Multiplication property of equality.
Simplify

Subtraction property of inequalities
Simplify
Division property of inequalities
Simplify