(i)

a = -9, d = -14 + 9 = -5

a₃₀= a + 29d

= -9 + 29(-5) = -154

a₂₀= a + 19d

= -9 + 19(-5) = -104

a₃₀ – a₂₀= -154 – (-104)

= -154 + 104

= -50

(ii)

a = a, d = a + d – a = d

a₃₀= a + 29d

a₂₀= a+ 19d

a₃₀ – a₂₀ = a + 29d – a – 19d

= 10d