In order to get a horizontal asymptote, the degree of the numerator and denominator must be the same. In this case, they are the same because both would have an x² term as their largest exponents.
When that is true, the value of horizontal asymptote is found by dividing the coefficients of those leading terms. The numerator would have a leading term of kx² over the denominator's leading coefficient of 14x². That means that:
------- = 2
Multiplying both sides by 14x² to eliminate the fraction, you get:
kx² = 2(14x²)
kx² = 28x²
k = 28
I hope that helps!! :-)