b = number of beetles
r = number of birds
s = number of spiders
"She has an equal number of beetles, birds and spiders". That means b = r = s. They all stand in for the same number, and that number being some positive whole number.
One spider has 8 legs, so s of them have 8s legs. One beetle has 6 legs, so b of them have 6b legs. One bird has 2 legs, so r birds have 2r legs.
In total, all of the animals have 6b+2r+8s legs. We'll replace r and s with b, since earlier we were given that b = r = s.
So we end up with:
6b+2r+8s
6b+2b+8b
(6+2+8)b
16b
The number of legs of all the animals is equal to 16 times the number of beetles. Set this equal to 270 and isolate b
16b = 270
b = 270/16
b = 16.875
We run into a problem. It's not possible to have the variable b equal to a non-whole decimal number like this. It's possible your teacher made a typo somewhere. I would ask them for clarification.