Which best explains why all equilateral triangles are similar?
a. all equilateral triangles can be mapped onto each other using dilations.
b. all equilateral triangles can be mapped onto each other using rigid transformations.
c. all equilateral triangles can be mapped onto each other using combinations of dilations and rigid transformations.
d. all equilateral triangles are congruent and therefore similar, with side lengths in a 1: 1 ratio.

A. All equilateral triangles can be mapped onto each other using dilations.

Step-by-step explanation:

We know that all equilateral triangles are similar to each but not congruent because they all have same measure of corresponding angles 60° but do not have same side-lengths.

So, equilateral triangles can be mapped onto each other using dilation because they maps similar shapes (sometimes congruent) where as rigid transformations always map congruent shapes so we cannot map all equilateral triangles by using  rigid transformations.

n=9

step-by-step explanation:

7 times a number = 7n

decreased by 13 = 7n-13

same as is =

5 times the number = 5n

increased by 5 = 5n+5

7n-13 = 5n+5

2n=18

n=9