But 4.48V applies only to line 2.In line 2 the voltage is 4.48, I was asked "when A is connected to C and A is positive, to work out the voltage of R3, the currents of R1 and R2 and the value of R3." and was given a diode value of 0.7 V.
How did you determine R1 and R2?
The other question to ask is, why are all the voltages different?