Answer:
t = b + n
Explanation:
for the 2 lines to be parallel then their slopes must be equal
calculate the slope m using the slope formula
m =

with (x₁, y₁ ) = (x₁, a + n ) and (x₂, y₂ ) = (x₂, t ) ← 2 points on line k
m =
=

repeat with
(x₁, y₁ ) = (x₁, a ) and (x₂, y₂ ) = (x₂, b ) ← 2 points on line j
m =

equating the 2 slopes gives
=

since the denominators are the same on both sides, then equate the numerators
t - a - n = b - a ( add a to both sides )
t - n = b ( add n to both sides )
t = b + n