5 radios = $50 each
so the whole radios cost 5 x 50 = $250
he sold three at a 20 % profit
so by way of ratio
100% = $150
120% = x
x = (120 x 150)/100
x =$180
he then sold the other two and made a 20% loss
so
100% = $100
90% = y
y = (100 x 90)/100
y =$90
so his net sales = 180 + 90 = $270