Use table tag to align it.
<table>
<ul class="nav">
<tr>
<td>
<li class="whoweare">
<img src="images/cars.png"><a href="#">CARS</a></li>
</td>
<td>
<li class="services">
<img src="images/jobs.jpg"><a href="#">JOBS</a></li>
</td>
<td>
<li class="contact">
<img src="images/services.jpg"><a href="#">SERVICES</a></li>
</td>
</tr>
</ul>
</table>