\(12,5-x:4=7,6\\ x:4=12,5-7,6\\ x:4=4,9\\ x=19,6\)

\(8x+2x=25.22\\ 10x=550\\ x=55\)

\(\left(5x^3-2x^2+\dfrac{1}{3}x\right)\left(-\dfrac{3}{2}x^3\right)\\=-\dfrac{15}{2}x^6+3x^5-\dfrac{1}{2}x^4 \)

a. \(6x^2-3xy=3x\left(2x-y\right)\)

b. \(x^2-y^2-6x+9\\ =\left(x^2-6x+9\right)-y^2\\ =\left(x-3\right)^2-y^2\\ =\left(x-3-y\right)\left(x-3+y\right)\)

c. \(x^2+5x-6\\ =x^2+6x-x-6\\ =x\left(x+6\right)-\left(x+6\right)\\ =\left(x-1\right)\left(x+6\right)\)

\(\dfrac{7}{8}\)

B