the total cost of a watch and a radio is rs 500 .If the watch is cheaper than the radio by rs 150,find their cost

Let cost of watch=w
Let cost of watch=r

w+r=500
but w=r-150

So;r-150+r=500
2r=500+150
2r=650
r=650/2
r=325

If r=325,
then w+r=500
w+325=500
w=500-325
w=175

Cost of watch=rs175
Cost of radio=rs325