Question 12
Positive integers are arranged in the array as shown below. What is the sum of all the integers located on the fourth row?
$$\begin{array}{ccccc}&&1&&\\&2&3&4&\\5&6&7&8&9\\&&\cdots&&\end{array}$$
$$\begin{array}{ccccc}&&1&&\\&2&3&4&\\5&6&7&8&9\\&&\cdots&&\end{array}$$