Does anyone know how to fix this formula, it doesn't work!!?

=IF(S7<"75%","0%",IF(OR(S7 = "75%:79.9%"),U2 = T7*50%,IF(OR(S7 = "80%:84.9%"),U2 = T7*70%,IFORS7 = "85%:89.9%"),U2 = T7*80%,IF(OR(S7>"89.9%",U2 = T7))))))