Find constants of ideal op amp circuit problem
You are trying to find the transfer function, not the actual voltages.

To figure that out, find the gain of the path from Uin to Uout.

U1 has a gain of \$ \frac {Rf} {R1} +1\$ which yields a non-inverting gain of 3.67 

U2 has a gain (from U1) of -1 and so does the final amplifier, so the total gain (from Uin) is 3.67.

Then we take Uin2 which goes to a summing junction and the total gain to Uout from Uin2 is +1 (from -1 * -1).

So the transfer function is Uout = (Uin * 3.67 ) + Uin2 which is (Uin * 3.67) + 1V

Therefore A = 3.67 and B = 1