Algebra

First we can label some of the variables. 

a = 2 because it is the coefficient of \(x^2\).

\(2(x - h)^2 + k\)  and we can now foil \((x - h)^2\)

We foil it into \(x^2 + h^2 + 2xh\) and we have to multiply that by 2. We can see now that 4hx = 6x in the expression in the question getting: 

\(h = 1.5\)

This is valid because we are not given the value of variable k.