How can you determine if two lines are perpendicular based on their y=mx+b equations?

What is the ratio for the surface areas of rectangle prisims shown below given that they are similar and that the ratio of their edge lengths is 7: 3

Miranda is braiding her hair.then she will attach beads to the braid.she wants 1_3 of the beads to be red.if the greatest number of beads that will fit on the braid is 12,what other fractions could represent the part of the beads that are red?

Can some one me with these questions