Are you sure you don't mean: the 2 orca whales add up to 13,000 lbs?
Because I'm getting an odd answer...
Let be the weight of a beluga whale
Let be the weight of an orca whale
You know: "The weights of two beluga whales and 3 orca whales add up to 36,000 pounds"
And: "...one of the orcas add up to 13,000 lbs."
We have 2 orca whales, so their weight is two times the weight of one.
So its weight is: .
Use the value of to get the weight of one beluga whale.
A negative weight? I don't see how... ?