Early backers of business-to-business (B2B) manufacturing platform Zetwerk are sitting on up to 36x returns post listing on Friday, with four venture capital firms and an affiliate realising about Rs 1,215 crore through the IPO.The listing provides liquidity for investors who backed an industrial business when venture funding largely favoured software and consumer internet companies.The shares closed at Rs 138.30 on the BSE, 8.4% below the Rs