In an xy-coordinate plane, a line is defined by y = kx + 1. If (3, b), (a, 4), and (a, b+1) are three points on the line, where a and b are unknown, then k = ?  Pick one.
A) 1/2	B) 1	C) 3/2	D) 2/3	E) 5/2
b=3k+1...(1)   b+1=ak+1...(2)   4=ak+1...(3)   Taking (2) and (3)   4=b+1   b=3   Taking (1)   3=3k+1   k=2/3   Answer : 2/3
<result>D</result>
In an xy-coordinate plane, a line is defined by y = kx + 1. If (3, b), (a, 4), and (a, b+1) are three points on the line, where a and b are unknown, then k = ?