Anyone kurt is financing a $315,000 mortgage for 30 years at a fixed rate of 7.35%. what is the total cost of the principal and interest after 30 years? $651,078.00 $676,305.00 $781,293.60 $788,489.94

Loan Cost Total = (r * p * n) / [1 -(1 +r)-n]
See attached graphic
rate gets divided by 1,200 = 0.006125
n = number of payments = 30 * 12 = 360

Loan Cost Total = (.006125 * 315,000 * 360) / [1 - (1.006125)^-360]
Loan Cost Total = ( 694,575 ) / [1 - ( 0.1109944992 )
Loan Cost Total = 694,575 / 0.8890055008
Loan Cost Total = 781,294.38

Considering all the rounding in the calculations, it seems that answer "C" 781,293.60 is really close.  (78 cents lower than what I calculated).

Source:
http://www.1728.org/loanfrm4.htm

Ok here we go ..there are plenty of ways to solve such math problems but we will go for the smartest and easiest ..5x+2y=7  -2x+6y=9we rearrange them into the following ..by multiplying the 1st equation by 2 it becomes 10x + 4y = 14we rearrange it and so it becomes 10x = 14 - 4yas for the second equation we multiply it by 5 and rearrange it so it becomes as to the following ..-10x + 30y = 45rearranging so 10x = 30y -45now 10x equals both 14 - 4y and 30y -45so   14 - 4y = 30y -4531 = 26yy= 31/26 = 1.19 or around 1.2so by now we can calculate x easily as  -2x+6y=9so 2x = 6y -9 = 6 * 31/26 - 9 = -1.84  then x = - 0.92 or around -0.9best luck!