Question

How do i solve for all the missing side lengths?

Answer 1

I think you multiply 12 and 16, then divide it by 2
which is 192 divided by 2 
=96

Answer 2

So hmm check the picture below


notice, dropping a perpendicular line to the opposite side, of the right-angle, gives three similar triangles, a small, a medium, and the large one containing the other two

now, let's use the medium and small triangles then, with proportions

$\bf \cfrac{medium}{small}\qquad \cfrac{12}{x}=\cfrac{16}{12}$

solve for "x"