A simple question ( i think ) working out cuboid

if the sum of all edges of a cuboid is 4.8
and b = 2/3a
v=abc
4.8=4(a+b+c)

( as in, two 3rds of A)

how long does a, b and c have to be to make the biggest volume possible



I really dont understand how to do this....

i was wondering if someone could explain to me how i go about doing this? a breif break down of how to flow through and do it? :-)
thanks so much for any help

this is all i have.... i know its completely wrong


v=abc

4.8=4(a+b+c)

4a + 4b + 4c = 4.8

a + b + c = 1.2

b = 1.2 - a - c

b = 2/3a

2/3a = 1.2 - a - c

you have 3 equations, 4 unknowns, you should be able to make V a function of one of those variables say a, then set the first derivative to 0 to get a where V is largest (which should be there in this case)