How would I determine if this is right or not ?

the answer is C. 3, 4, 5
because they form
[tex] {3 }^{2} + {4}^{2} = {5}^{2} [/tex]
but the other choices don't follow the same rule fir their numbers.
You use the pythagorean theorem to check
Square the smaller sides 3 and 4, then add those results up
3^2 = 9
4^2 = 16
9+16 = 25
Note how this is equal to the value of 5^2 which is squaring the longest side of the 3-4-5 triangle.
Another way you can write it down is like this
a^2 + b^2 = c^2
3^2 + 4^2 = 5^2
9 + 16 = 25
25 = 25