You dont need tocreate a function.

A easier way using only EXEC :

EXEC('SELECT CAST(

(1.66 * 300 / 1170)

+ (1.75 * 220 / 1170)

+ (1.791 * 0 / 1170)

+ (1.6666 * 100 / 1170)

+ (1.96 * 350 / 1170)

+ (1.8716 * 100 / 1170)

+ (1.6666 * 0 / 1170)

+ (1.44 * 100 / 1170)

AS DECIMAL(18,4))')