IF B what? B1, B100, ??? You need to write the formula using cell references with the column letter and row number.
For example: =IF(B1<400,H1*L1*150,H1*L1*160)
What happens if the value is =400? In this example, it'll use the latter calculation.
Syntax is: =IF(logical_test,action_if_true,action_if_false)