Please answer a question about the following article about University of Notre Dame:

The Rev. Theodore Hesburgh, C.S.C., (1917–2015) served as president for 35 years (1952–87) of dramatic transformations. In that time the annual operating budget rose by a factor of 18 from $9.7 million to $176.6 million, and the endowment by a factor of 40 from $9 million to $350 million, and research funding by a factor of 20 from $735,000 to $15 million. Enrollment nearly doubled from 4,979 to 9,600, faculty more than doubled 389 to 950, and degrees awarded annually doubled from 1,212 to 2,500.

In the time that Hesburgh was president of Notre Dame by what factor did the operating budget increase?
18