What is the value of a in the diagram below?

a=8

Step-by-step explanation:

We can use ratios of similar triangles to solve

The smaller triangle has sides a and 12  and the larger triangle has sides a+a+4  and 12+18  which combine to 2a+4  and 30

a               2a +4

=

12            30

Using cross products

30a = 12(2a+4)

30a = 24a +48

Subtract 24a from each side

30a -24a = 24a-24a +48

6a = 48

Divide each sdie by 6

6a/6 =48/6

a =8

idk

step-by-step explanation:

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