For starters you don't need the sum bit to multiply two cells together. It should just be =A1*B1. Sum is used to add the contents of two cells together.
I presume you want the answer to be 148 hours * �6.00 = �888.00. If this is the case your formula would need to be
(A1*24)*B1
You are having a problem because Excel cannot multiply the two formats together and by multipling (A1) by 24 you are converting the date to its decimal equivilant. Once it is a decimal it can then be multiplied by (B1) also in decimal.