Question 812589
{{{a/7 + 1/4 = 5/6}}}
make all the denominators the same
{{{(a/7) * (12/12) + (1/4) * (21/21) = (5/6) * (14/14)}}}
{{{12a/84 + 21/84 = 70/84}}}
since all the denominators are the same, multiply the whole equation by that denominator to get rid of it
{{{84(12a/84 + 21/84) = 84(70/84)}}}
{{{12a + 21 = 84}}}
{{{12a + 21 - 21 = 84 - 21}}}
{{{12a=63}}}
{{{(12a)/12=63/12
{{{a=63/12}}}
{{{a=21/4}}}