6: -8+4V
8: -9-15V OR -9+(-)15V
10:-17+33V
Y = -2 x - 9
3 x - 4(-2 x - 9 ) = -8
3 x + 8 x + 36 = - 8
11 x = - 44, x = - 4
y = 8 - 9 , y = -1
This is a unique solution, the system is independent.
16,500
60 minutes in an hour / 12 minutes = 5
5 * 3,300 = 16,500
Recall the Maclaurin expansion for cos(x), valid for all real x :

Then replacing x with √5 x (I'm assuming you mean √5 times x, and not √(5x)) gives

The first 3 terms of the series are

and the general n-th term is as shown in the series.
In case you did mean cos(√(5x)), we would instead end up with

which amounts to replacing the x with √x in the expansion of cos(√5 x) :
