If a 250-g mass is hung on two identical springs, hung side by side , and both support the 250-g mass, how much will each spring stretch?

There's no way we can calculate how much the springs will stretch, because we don't know their "spring constants" ... how far 1 Newton of force will stretch each spring.

But we do know that both springs will stretch the same amount, because they're identical and they share the load equally.

So ...

The weight of the load is (mass) x (gravity) = (0.25 kg) x (9.81 m/s²) = 2.4525N

Each spring supports half of the load = 1.22625 N

If ' k ' is the spring constant of each spring, then each spring stretches by

1.2265/k  meters .

see earlier