Draw six dots then a plus sign then draw seven dots and the count them and put an equal sign and however many dots. Doe the same with the other numbers
Option I
(3x+4)cm =(2x+10)cm
3x-2x=6
x=6
Option II
(3x+4)= (x+12)
3x-x=12-4
2x=8
x=4
Option III
(2x+10)= (x+12)
2x-x=12-10
x=2
F^1(-2) = 2(-2) = -4
f(-4) = 1/2 * -4 = -2
f(f^-1(x)) = x so answer is -2
Try, please, this:
1) Imagine, that pharmacist used 'x' gr. of 40% solution and 'y' of 70% solution.
Together (20 gr. of 52% sol.) it will be x+y=20.
2) From other side, the pharmacist combined 40x and 70y gramms, after obtaining together it is 52(x+y) gramms. In other words 40x+70y=52(x+y)
3)

Answer: 8 gr. of 70% solution and 12 gr. of 40%.