Question 1055682
You didn't really need the LCD to start.
X terms on one side.
Constant terms on the other.
{{{b/a - (d/c)x = (a/b)x - c/d}}} 
{{{(a/b)x+(d/c)x=b/a+c/d}}}
{{{(a/b+d/c)x=b/a+c/d}}}
{{{x=(b/a+c/d)/(a/b+d/c)}}}
Now multiply numerator and denominator by the LCD.