If by profit 50% you mean profit = commodity cost *50%,

Net income = 20/3 = 6.7W

Excluding 7W expenses, the monthly balance is 6.7-7 =-0.3W..

If by profit 50% you mean profit = turnover *50%,

Net income =20/2= 10W

Excluding the expenses of 7W, the monthly balance is 10-7=3W.