Question 1055496
Find the rate of both arrays,
{{{R[1]*5=6}}}
{{{R[1]=6/5}}}
and
{{{R[2]*7=15}}}
{{{R[2]=15/7}}}
So after 3 months, array 1 has generated,
{{{(6/5)*3=18/5}}}
So then both together need to generate X to reach 30.
{{{18/5+X=30}}}
{{{X=150/5-18/5}}}
{{{X=132/5}}}
So then together,
{{{(R[1]+R[2])t=132/5}}}
{{{(6/5+15/7)t=132/5}}}
{{{t=(132/5)/(6/5+15/7)}}}

{{{t=((132/5)(7/7))/((6/5)(7/7)+(15/7)(5/5))}}}
{{{t=(924/35)/(42/35+75/35)}}}
{{{t=(924/35)/(117/35)}}}
{{{t=924/117}}}
{{{t=308/39}}} or approximately 7.9 months.