Complex power, real power
I believe there are two issues preventing you from matching the answer key.

The first is that they really only want the power in Za, so you need to calculate U.  Just take your current (I agree with that calculation) and multiply it by Za

U = I \$\cdot\$ (40 + j30)

Then calculate S = I \$\cdot\$ conj( U ).  The real part of this should be 569 W.  Now, that's still double what the book has...

So I would assume that the Uq given is peak voltage instead of the usual default of RMS.  That reduces I_RMS by \$\sqrt2\$ and U_RMS by \$\sqrt2\$, reducing the product by a full factor of 2.