Answer:
Let's start by using algebra to solve for the original amount that Alex paid for his shares.
Let X be the original amount that Alex paid for his shares.
We know that his shares dropped in value by 35%, so after the drop, he had 65% of his original investment left:
0.65X = $72,800
Solving for X:
X = $72,800 / 0.65
X = $112,000
Therefore, Alex paid $112,000 for his shares to begin with.