Alan

Like so:

".... If  ?  students take only Spanish ..."  The number of students taking only Spanish is missing,

I suspect this is what was meant:

As follows:

Perhaps it's easier to see in degrees:

1 radian = 57.3 degrees

2 radians = 114.6 degrees

-7 radians = -401.1 degrees  This has rotated clockwise by more than 360 degrees.  How much more?  -41.1  So it's in the fourth quadrant.

-9 radians = -515.7 degrees.  This has also rotated clockwise by more than 360 degrees.  How much more?  -155.7.  This place it in the third quadrant, which doesn't match any of the points on your diagram!

x = k/r 

Given  5 = k/25 then k = 5*25

Hence x = 5*25/40

Where is the truth table?

1.  Add the two equations to get $2a^3=1352$,  so  $a=26^{2/3}$

2. Subtract the two equations to get $6ab^2=6$  so $ab^2=1$

Hence $b^2=26^{-2/3}$  and $b=\pm26^{-1/3}$

Take it from there!

x/(x - 5) = 4/(x - 4) + 12/(x^2 - 9x + 20)

Note that x^2 - 9x + 20 can be written as (x-5)(x-4), so multiply all terms by   (x-5)(x-4) to get

x(x-4) = 4(x-5) + 12, or x^2 -4x = 4x -20 + 12  or  x^2 - 8x +8 = 0.  

Use the quadratic equation to find the values of x.

Like so: