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 1
Therefore we have
10x /100 + (7000 -x)*7/100= 580
Multiplying both sides by 100
10x+(7000-x)*7 = 58000
simplifying
10x+ 49000 - 7x = 58000
3x = 58000-49000
3x = 9000
x= 3000
therefore the sum of money invested at 7% = 7000 - 3000 = 4000