Different calculations in EXCEL and TERADATA SQL
Teradata rounds after each calculation based on the resulting datatype (Standard SQL compliant), to get the expected reault you can either CAST the 1st operand to a NUMBER (no need to think about precision) and finally back to DECIMAL:

Cast((Cast(75 AS NUMBER)/979.86) *979.86 AS DECIMAL(10,2))


Ot you rearrange the order of calculation to multiply first and then divide:

979.86 * 75 / 979.86