Well, you know that a triangle has 180 degrees, and we've accounted for 90 + 58 = 148 of them. Thus, the remaining angle is 42 degrees.

I'll call your "bottom" side x, your "vertical" side y, and your hypotenuse h (if I'm reading your description right!.

So, \(\displaystyle sin(58) = \frac{x}{h} \)

But we know x = 4, so

\(\displaystyle sin(58) = \frac{4}{h} \).

Can you find y?

Edit: All angles are in degrees.