By Sachin Ravikumar and Shanima A (Reuters) -M&C Saatchi on Tuesday rejected a fourth takeover offer from its biggest investor Vin Murria, saying the “derisory” proposal worth 253.6 million pounds ($316.4 million) undervalued the British advertising group’s business. Software entrepreneur Murria’s acquisition vehicle AdvancedAdvT announced the fresh offer earlier, giving M&C investors a choice between receiving 2.530 new AdvancedAdvT shares for each share held or a mix of cash and shares. Based on AdvanceAdvT’s last closing share price, both options value M&C Saatchi at 207.5 pence per share, …