The last condition gives you that the center of the ellipsoid will be in (0,0,0). So the equation of this ellipsoid will be:$\frac {x^2} {a^2} +\frac {y^2} {b^2}+\frac {z^2} {c^2}=1$You have 3 points. Put them into this equation and get 3 equations and 3 unknowns - $$a,b,c$$ and then solve it and get the answer.