The fourth term of the sequence is $3^0+ 3^1+ 3^2+ 3^3$. I can use the exponent rules to simplify this expression. First, I know that $3^0=1$, so I can replace that with 1. Next, I know that $3^1=3$, so I can replace that with 3. Then, I know that $3^2=9$, so I can replace that with 9. Finally, I know that $3^3=27$, so I can replace that with 27. Now I have $1+3+9+27$. I can add these numbers from left to right. First, $1+3=4$. Then, $4+9=13$. Finally, $13+27=40$. So the simplified value of the fourth term of the sequence is 40. 
Consecutive powers of 3 are added to form this sequence: $3^0,3^0+ 3^1, 3^0+ 3^1+ 3^2$, and so on. What is the simplified value of the fourth term of the sequence?