3+1 + - + ... ?

What is the sum of the first 7 terms of this geometric series: 3+1 + 3

15

Step-by-step explanation:

3+1+3+1+3+1+3 = 15 this is what it would look like if you write it out. To save time do 3 times 4 to get 12 and then just add three ones to 12 to get 15.