If a scale factor of 1/4 is used to make a reduction, what is the base of the reduced triangle?

You have not attached the image, therefore, I cannot provide an exact answer.
However, I will tell you how to solve this problem and you can apply on the numbers you have.

Assume that the base of the original triangle has a length of x units.

Applying a scale factor of 1/4 means that all new dimensions of the triangle will be reduced to 1/4 of their original value.

Based on this, 
the base of the new triangle after applying 1/4 scale factor would be (1/4)*x which is equal to 0.25x

Hope this helps :)