Answer:
13)
A minim (half note) is worth two beats
A dotted crotchet (dotted quarter note) is worth one and a half beats
So, we need a quaver (eighth note) to make it work two beats
14)
A minim (half note) is worth two beats
A crotchet (quarter note) is worth one beat
We need another crotchet (quarter note) to make it work two beats
15)
A crotchet (quarter note) is worth one beat
A quaver (eighth note) is worth 1/2 of a beat
So we need another quaver (eighth note) to make it worth one beat
16)
A semibreve (whole note) is worth four beats
A crotchet (quarter note) is worth one beat
So we need a dotted minim (dotted half note) to make it worth four beats