Which equations have infinitely many solutions?

Which is the equation of a line perpendicular to the line with the equation 3x+4y=8

Two cyclists 84 miles apart start riding toward each other at the samen time. one cycles 2 times as fast as the other. if they meet 4 hours later what is the speed (in miles) of the faster cyclists

Ab and bc form a right angle at point b. if a= (-3,-1) and b= (4,4) what is the equation of bc?