8Similar triangles ratio

Triangle ABC is similar to triangle DEF, with AB = 6, BC = 9 and DE = 10. Find EF.

Since AB matches DE and BC matches EF, the ratio 6/10 = 9/EF gives EF = 15. Cross-multiplying: 6·EF = 90, so EF = 90/6 = 15, checked by 6/10 = 9/15 = 0.6.