Answer:
K = x⁶ will be the substitution.
Step-by-step explanation:
The given equation is 
Now we have to convert it in a quadratic equation which should be in the form of 
We can rewrite the equation as
4(x⁶)² - 5(x⁶) - 14 = 0
Now we are clear that we have to substitute x⁶ = k to convert the equation in a quadratic equation
4K² - 5K - 14 = 0
Therefore, K = x⁶ will be the substitution.