Question 983400
Original amounts are a and b for how many in cartons a and b.


{{{a+b=324}}}


Sold  some leaving {{{4/7}}} of the number in carton a, so this means carton a had  {{{(4/7)*a}}} now in carton a.


Twice as many now in carton a than in carton b:
{{{((4/7)*a)/b=2}}}
-
{{{(4a)/(7b)=2}}}


{{{4a=2*7b}}}


{{{2a=7b}}}


System to solve:
{{{system(a+b=324,2a=7b)}}}


More than one way to solve.  

{{{a=324-b}}}, (choosing substitution)
-
{{{2(324-b)=7b}}}
{{{2*324-2b=7b}}}
{{{648=9b}}}
{{{highlight(b=72)}}}


You can find a.