a) The question asks you for the angle for the first 2 orders, meaning the 1st order of diffraction and the 2nd order of diffraction, not the 2nd order alone.

The angle for the second order is good.

b) Right, you have 5 orders below the 0 order diffraction. Therefore, you also have 5 orders above the 0 order diffration, for a total of 5 + 1 + 5 = 11 diffraction orders.