How many vector::push_back() operations are performed between lines 8 and 13 when this code is executed? The size of the input is the number of elements n in the vector v. Replace the question marks in the formula with appropriate entries based on the code. Then fill in the box with an expression involving just n and constants. 

Here is an algorithm implemented in C++. 1 vector products (const std::vector &v) { 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 } vector pre; vector suf; int i; int n = v.size(); pre.push_back (v [0]); suf.push_back (v [n-1]); for (i } 1; i < n; ++i) { pre.push_back (pre. back() * v[i]); suf.push_back (suf.back() * v[n - i - 1]); reverse (suf.begin(), suf.end()); vector result (n); result [0]=suf [1]; result [n-1] for (i = } pre [n - 2]; 1 ; i < n-1; ++i) { = result [i] return result; = pre [i-1]* suf [i + 1];