X+3y=-13
x=-3y-13
5(-3y-13) +7y = -9
-15y -65 +7y = -9
-8y-65=-9
65 -
-----
-74
/-8
------
y= 9.25
x+3(9.25) = -13
x+27.75= -13
27.75-
-------
x= -40.75
I hope this helps you out
You would take 6.4% into 1640000 and you would pay that the next 30 years