Complex sentence: It was Haider who gave Lata Mangehskar her major break in Hindi films with "Majboor" (1948) and took 19 year old Lata to S. Mukherjee to sing in "Shaheed" (1948) but Mukherjee rejected her voice sayoing it was too thin !
Split into simpler sentences: It was Haider who gave Lata Mangeshkar her major break in Hindi films with "Majboor" (1948). He took 19 year old Lata to S. Mukherjee to sing in "Shaheed", but Mukherjee rejected her voice saying it was too thin!