(b)

Given,

(i) 6a² + 2

(ii) -3a² + 3a

(iii) -2a +3

Now, (i) + (ii) + (iii)

= 6a² + 2 – 3a² + 3a – 2a + 3

Add the like terms,

= 6a² – 3a² + 3a – 2a + 2+ 3

= 3a² + a + 5

Also, (ii) – (i)

= -3a² + 3a – (6a² + 2)

Opening the brackets,

= -3a² + 3a – 6a² – 2

Subtracting the like terms,

= -9a² + 3a – 2

and (iii) – (i)

= -2a + 3 – (6a² + 2)

Opening the brackets,

= -2a + 3 – 6a² – 2

Subtracting the like terms,

= -6a² – 2a + 1

(c)

Given,

(i) 9m² – 2mn + n²

(ii) m² + n²

(iii) m² – 3mn – 2n²

Now, (i) + (ii) + (iii)

= 9m² – 2mn + n² + m² + n² + m² – 3mn – 2n²

= 9m² – 5mn + 2n² + 2m² – 2n²

Add the like terms,

= 11m²– 5mn

Also, (i) – (ii)

= 9m² – 2mn + n² – (m² + n²)

Opening the brackets,

= 9m² – 2mn + n² – m² – n²

Subtracting the like terms,

= 8m² – 2mn

and (ii) – (iii)

= m² + n² – (m² – 3mn – 2n²)

Opening the brackets,

= m² + n² – m² + 3mn + 2n²

Subtracting the like terms,

= 3n² + 3mn