Walt made an extra $7000 last year from a part-time job. He invested part of the money at 10% and the rest at 7%. He made a total of $580 in interest. How much was invested at 7%?Select one:

We know that Interest= PNR/ 100. where P is the principal R is the rate of Interest  N is the no of years the sum has been invested for. Since N  is not given we assume that to be 1Therefore we have 10x /100 + (7000 -x)*7/100= 580Multiplying both sides by 10010x+(7000-x)*7 = 58000simplifying10x+ 49000 - 7x = 580003x = 58000-490003x = 9000x= 3000 therefore the sum of money invested at 7% = 7000 - 3000 = 4000