Solve a recurrence relation with two recursion calls using the iteration method
Hint: Let $S(n) = T(n+1) + T(n)$. We have $S(0) = 1$, and for $n &gt; 0$,
$$ S(n) = T(n+1) + T(n) = [3T(n) + 4T(n-1)] + T(n) = 4(T(n) + T(n-1)) = 4S(n-1). $$
Can you take it from here?