2010 GRE Paper Based Test Section 6(Verbal) Q12,Q13 and Q25

Hi Guys,

Need help understanding how to form equation for this question.

*Q12
Last year Kate spent between 1/4 and 1/3 of her gross income on her mortgage payments. If Kate spent $13,470 on her mortgage payments last year, which of the following could have been her gross income last year?

Does this mean [(1/4) + (1/3)]*gross = 13,470?

*Q13(Need help in understanding steps to solve this question)

In State X, all vehicle license plates have 2 letters
from the 26 letters of the alphabet followed by 3 one-digit numbers. How many different license
plates can State X have if repetition of letters and
numbers is allowed?

*Q25(Need help in understanding steps to solve this question)
The figure shows line segment PQ and a circle with radius 1 and center (5, 2) in the xy-plane. Which of
the following values could be the distance between
a point on line segment PQ and a point on the
circle?

image

Thank you!