Working out intervals in the alto clef can be awkward if you don’t read the clef fluently. If you are not fast at working in alto clef, it’s usually better to work everything out in the treble clef first. Make sure you have some scrap paper to hand before you start your exam.
Here are some examples.
Write the note a minor 6th higher than this note.
This note is F#. Put an F# onto a treble clef stave. Work out the note a minor 6th higher – that’s D natural.
Put in the D natural on the alto clef stave.
Here is a different question.
Name this interval.
The notes are A and Eb. Put them into the treble clef, and work out the scale of A major.
The interval A to E natural is a perfect 5th because it’s in the A major scale. A-Eb is one semitone narrower, so it must be a diminished 5th.