Franco made dozen muffins for his party. Upon taking them out of the oven, he noticed that two muffins were badly burned. Franco served 7/10 of the remaining muffins. Which equation shows the fraction of non-burned muffins that remain?

$12. that is my answer.

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4

answer is because 4×10=40

and 98×4= is 392

40,392