Question 159839
X=unknown #
-X= unknown # additive inverse

The equation is 

-X/12=3/x-1

Find a common denominator 12X

Multiply each term by 12X

-X^2=3(12)-12x

This is a quadratic equation

add X^2 to both sides and solve*[invoke solve_quadratic_equation 1, -12, 36]

Replace x with 6

-6/12=3/6-1

-1/2=1/2-2/2
-1/2=-1/2