Verified answer

You just need to combine those three equations in a way that gives you the answer you desire. Remember that when you multiply or divide an equation by some number, you multiply or divide ΔH by the same number. Also, if you flip an equation over, you change the sign on ΔH.

Now, the equation in your question is not balanced. I would be tempted to balance it as:

2 NO + O2 --> 2 NO2

(If you have some other equation than this, you'll need to alter my answer here, but you should be able to use the same process.)

Now, since you need NO on the left and only the third equation has NO in it, multiply that equation by 2:

2 NO + 2 O3 --> 2 NO2 + 2 O2 ΔH = -398 kJ

now, you need to get rid of the O3 on the left, so flip the top equation over:

3 O2 --> 2 O3 ΔH = + 427 kJ

When you add those two equations together, you have:

2 NO + 3 O2 + 2 O3 --> 2 O3 + 2 NO2 + 2 O2 ΔH = 29 kJ

Just cancel everything that is the same on both sides and you have:

2 NO + O2 --> 2 NO2 ΔH = 29 kJ