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?

triangle base Thanks in advance

Do you know about similar triangles? – JohnD Nov 24 '14 at 04:30 — JohnD, Nov 24 '14 at 04:30
Surely what OP is asking is clear. – André Nicolas Nov 24 '14 at 06:01 — André Nicolas, Nov 24 '14 at 06:01

score 0 · Accepted Answer · answered Nov 24 '14 at 04:07

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 $11.25$

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