Build a VHDL calculator

Using UART communication interface code, need to program Xilinx FPGA spartan 6E where it should be able to transmit and recieve data via putty. Then build calculator on FPGA so that for example if send 4 +5 to FPGA via putty, the FPGA should transmit 9 to putty. So far, I have a test bench to analyse the simulation produces on sim, xilinx software. The test bench shows that receiving is working but the transmission is not. I need help with it and the calculator. My deadline is 6th May.