Assuming your hours start in A1, put this in B1
=A1*50
select cell B1 again and move your cursor to the lower-right corner of B1
until it turns into a small + sign and then double-click, the formula will
fill down in all cells in B adjacent to a value in A.
Assuming data in A2 down,
Put in B2: =A2*50
Copy B2 down as far as required by dragging the fill handle (the solid
square at the bottom right corner of the cell).