A n+1 =2^ (a n ) -1 and a 1 =2 a. 3, 7, 127, 7217
b. 7, 11, 127, 7217
c. 11, 27, 127, 7217
d. 2, 3, 7, 127

It is for sure letter d

Step-by-step explanation:

Hope this helps

I would first rearrange the second equation to get x by itself

x+15=3y
x=3y-15

Then I would substitute 3y-15 in for x in the first equation. I would do this because x has the same value as 3y-15

4(3y-15)+20=5y
12y-60+20=5y
12y-40=5y
-40=-7y
5.7=y

Then plug y back into an equation to get x

x+15=3(5.7)
x+15=17.1
x=2.1

Hope this is correct :)