Vector Algebra

Let $$\overrightarrow a = {a_1}\widehat i + {a_2}\widehat j + {a_3}\widehat k$$ $${a_i} > 0$$, $$i = 1,2,3$$ be a vector which makes equal angles with the coordinate axes OX, OY and OZ. Also, let the projection of $$\overrightarrow a$$ on the vector $$3\widehat i + 4\widehat j$$ be 7. Let $$\overrightarrow b$$ be a vector obtained by rotating $$\overrightarrow a$$ with 90$$^\circ$$. If $$\overrightarrow a$$, $$\overrightarrow b$$ and x-axis are coplanar, then projection of a vector $$\overrightarrow b$$ on $$3\widehat i + 4\widehat j$$ is equal to: