I drew an imaginary line passing through point O and forming two right triangles, as seen in the attached image.

The angles at O must all add up to 180, so:

60 - b + 90 - b + a = 180

Combine like terms:

150 - 2b + a = 180

Add 2b to both sides:

150 + a = 180 + 2b

Subtract 180:

a - 30 = 2b

Okay, now what is this equation telling us? Well, if we start with a and make it smaller by 30, then it will be equal to twice b. We can see, then, that a must be much greater than b, making the answer E, a > b.