I’m going to assume that by “a^2b” you mean “ba^2”, because few teachers are that mean.

Rearrange:

3a^2 – a^2b – 3a + ab + 5b – 5b – 15/15

Simplify:

3a^2 – a^2b – 3a + ab – 1

Divide by ‘a’:

a (3a – ab – 3 + b) – 1

Reduce (3a – ab – 3 + b):

a (3 – b) – (3 – b) = (a – 1) (3 – b)

Therefore:

“a (a – 1) (3 – b) – 1” is your answer.

Unless you meant:

(ab – 3a + 5b – 15) / (15 + 3a^2 – 5b – a^2b)

Simplify the top:

(ab – 3a + 5b – 15)

Reverse distribution:

a (b – 3) + 5 (b – 3)

Group:

(a + 5) (b – 3)

Simplify the bottom:

(15 + 3a^2 – 5b – a^2b)

Rearrange:

(3a^2 – a^2b – 5b + 15)

Reverse distribution:

a^2 (3 – b) + 5 (- b + 3)

Group:

(a^2 + 5) (3 – b)

Show entire fraction:

((a + 5) (b – 3)) / ((a^2 + 5) (3 – b))

Because -(b – 3) = (- b – – 3) = (- b + 3) = (3 – b),

Therefore:

“-(a + 5) / (a^2 + 5)” is your answer.

I hope this helps!