How can I find Triangle base length?

Question

How can I find base length of the triangle in attached picture?

Can I use mid-segment theorem to find the base?

Thanks in advance

Answer 1

Since you know the base of the small triangle is parallel to the base of the large triangle you can set up proportions.

Which would give you $${8\over 5}={18\over x}$$ Which you could solve for x: $$8x=90\implies x={45\over 4}=11.25$$

So the base of the large triangle would be $11.25$