What is the length of DE ?? Thx :)

A; 10

Step-by-step explanation:

What we can see here is that the triangles are similar.

Hence, the ratio of their sides are equivalent.

Thus, mathematically;

ED/BA = DF/AC = BC/EF

what we want to calculate is ED = x

Thus;

x/15 = 12/18

Cross multiply;

18 * x = 12 * 15

18x = 180

x = 180/18

x = 10

a28=58

step-by-step explanation:

a1=a1+(n-1)d

a28= 4+ (28-1)2

a28=4+(27)(2)

a28=4+54

a28=58