If the distance between the parallel lines 3x+4y+7=0 and ax+y+b=0 is 1, the integral value of b is

Since the given lines are parallel. Slopes of the lines are equal so a=34 and the two lines are 3x+4y+7=and 3x+4y+4b=0.Distance between them is |7−4b|32+42=1⇒7−4b=±5⇒b=1/2 or 3