I am a little confused

Can you get me started on how to solve the simultaneous linear equations

$\displaystyle \langle V_1, V_4 \rangle = \langle V_2, V_4 \rangle = \langle V_3, V_4 \rangle = 0$

I am having a brain fart when thinking about how to go about this

This is what i have so far.

$\displaystyle V_1*V_4 ---> \begin{bmatrix}-0.5\\-0.5\\0.5\\-0.5\end{bmatrix} * \begin{bmatrix}a\\b\\c\\d\end{bmatrix} = 0$

$\displaystyle -\frac{1}{2}a + -\frac{1}{2}b + \frac{1}{2}c + -\frac{1}{2}d = 0 $

$\displaystyle -1a + -1b + 1c = d $

I am not sure what to do from here now or if this is even right so far