Question 53011
This one's easier to solve if you simplify a little before you multipy by the LCD.
{{{1/2-x/30=3(x+7)/90}}}
{{{1/2-x/30=(x+7)/30}}}
The LCD is 30, multiply both sides of the equation by the LCD and the denominators all cancel:
{{{30(1/2-x/30)=30((x+7)/30)}}}
{{{30/2-30x/30=30(x+7)/30}}}
{{{15-x=(x+7)}}}
{{{15-x=x+7}}}
{{{15-x-x=-x+x+7}}}
{{{15-2x=7}}}
{{{-15+15-2x=-15+7}}}
{{{-2x=-8}}}
{{{(-2x)/(-2)=(-8)/(-2)}}}
{{{x=4}}}