<PRE><B>Question 654733</B>
Starting with the original equation:
{{{x/7 + x/9 = 16/63}}}
we need to add the two x terms together.  In order to do that, we need to find the lowest common denominator (LCD) of x/7 and x/9.  Since 7 and 9 are relatively prime, the LCD is 7*9 = 63.
{{{(9/9)*(x/7) + (7/7)*(x/9) = 16/63}}}
{{{9x/63 + 7x/63 = 16/63}}}
{{{16x/63 = 16/63}}}
Multiply both sides by 63:
{{{63*(16x/63) = 63*(16/63)}}}
{{{16x = 16}}}
{{{x = 1}}}</PRE>