Answer:
d = 4
Explanation:
the nth term of an AP is
= a₁ + (n - 1)d
where a₁ is the first term and d the common difference
given a₄ = 27 , then
a₁ + 3d = 27 → (1)
Also
a₁ + a₄ = 42 ← substitute a₄ = 27
a₁ + 27 = 42 ( subtract 27 from both sides )
a₁ = 15
substitute a₁ = 15 into (1)
15 + 3d = 27 ( subtract 15 from both sides )
3d = 12 ( divide both sides by 3 )
d = 4