It's the same as gcf(gcf(75, 100), 175). In other words, you can first use Euclid's algorithm to find the gcf of 75 and 100; then you can calculate the gcf of the result with 175.
To help you get started, by Euclid's algorithm, the gcf of 75 and 100 is the same as the gcf of 75 and 25 (where 25 is the remnainder of the division of 100 / 75).
The GCF is 25.
The GCF of 75 and 175 is 25.
It is: 25
The GCF is 25.
The GCF is 25.
25
It is 25
It is: 75 plus 100 = 175
The GCF is 25.
The GCF is 25.
The GCF is 25.
The GCF of 25, 75, and 100 is 25. Since 25 is a factor of 75 and 100, it is automatically the GCF.