Solution
= Solution
Perpendicular <vectors> have zero <dot product>. Here $\mathbf u\cdot\mathbf v=3\cdot4-2c$, so $12-2c=0$. Therefore
$$
\boxed{c=6}.
$$
= Solution
Perpendicular <vectors> have zero <dot product>. Here $\mathbf u\cdot\mathbf v=3\cdot4-2c$, so $12-2c=0$. Therefore
$$
\boxed{c=6}.
$$