Step-by-step explanation:
similar triangles.
that means the angle are the same, and there is one common factor to multiply the lengths of all the lines of one triangle to get the lengths of the lines in the other triangle.
so,
5.1×f = 5.1 + 7.3 = 12.4 cm = BC
f = 12.4/5.1
and then, therefore
3.6×f = AC
3.6 × 12.4/5.1 = 8.752941176
so, AC is about 8.8 cm long
