im sorry i really i really wanted to answer but im going to need more information
4x -3y + z = -10...............(1)
2x +y + 3z = 0...............(2)
-x +2y - 5z = 17...............(3)
First we multiply 3*(2) and add it to (1)
6x +3y +9z =0..................+(1)..................> 10x + 10z = -10......(4)
Then we multiply -2*(2) and add it to (3)
-4x -2y -6z =0 ...................+(3)................> -5x -11z = 17...........(5)
Multiply 2*(5) and add it to (4)
-10x -22z = 34...................+(4).................> -12 z = 24 ..............>>> z = -2
Substitute z in (4)............> 10x +10(-2) = -10.............................>>> x = 1
Substitute x and z in (2).....> 2(1) +y + 3(-2) = 0..................>>> y = 4
Solution (x,y,z) = (1,4,-2)
2.5% of 15,00$ would be 375$. Assuming the "simple interest" is yearly, you would multiply 375 by 8, which is 3000$ :P (Another way to solve this would be to multiply the 2.5 by 8, which would be 20. and 20% of 15,000$ would also be 3,000$)
1.= 6,391
2.=6,3910
3. = 6,39100
All you do is add the 0s at the end