Find a vector v whose magnitude is 3 and whose component in the i direction is equal to the component in the j direction.
The vector $\displaystyle \vec p = i+j$ has the magnitude $\displaystyle |i+j| = \sqrt{2}$
Therefore the vector $\displaystyle \vec u = \frac1{\sqrt{2}} (i+j)$ has the magnitude 1. (It's a unit vector)
And therefore the vector $\displaystyle \vec v = 3 \cdot \frac1{\sqrt{2}} (i+j) = \left(\frac{3\sqrt{2}}2i + \frac{3\sqrt{2}}2 j \right)$