Question 1118395
b, by bus
c, by car
v, by van


The description is these three equations:
{{{system(9/20=b/(b+c+v),b/v=3,c=720)}}}


The first {{{9/20}}} proportion can be expressed as {{{9/20=(3v)/(3v+720+v)}}}.
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{{{highlight(v=270)}}}------go on from there.