It's been 40 years since I did one of these, but here is how I would proceed (and hoping someone else will correct this if I've got it wrong). Let's start the first one: 25" @2500 rpm FL90 ISA+5°.
First, 25" is the first line of each of the 3 ISA deviations of the table: -20, 0, and +20. So, so you're going to have to get an answer for 0° and +20° and then interpolate between the two to get +5°.
Let's get the answer for 0°, which means we won't use the 25" line but rather use FL90, which is 9000 feet. In the U.S. we don't (or at least didn't) use FLs, Flight Levels, below 18000, but in other countries they do. There is no 9000 feet entry, so you're going to have to get the answer for 8000 and 10000 and interpolate between the two.
So there are a set of answers for 8000, which you will have to interpolate between those and the set for 10000.
And then you'll have to get the answers for +20° and then do that interpolation.
Lazy man that I am, the only time I actually used these kind of tables accurately (or at least attempted to do so) was in taking exams. In actual practice I never did. Ball-parking the answers was always sufficient until I got to the airlines, and then all that was taken care of by the dispatchers.
So, for the exams, work several of these (in spite of their frustrating, time consuming nature), and develop an approach to doing them. Your most likely errors may well be in interpolating, which is why one approach in real life usage is to simply not interpolate but use the most conservative of the two values you would otherwise have interpolated between.
Really, the important thing is to not run out of fuel, which is why some might have called me "Tanker Terry."