How many strings of length 9 over the alphabet {0, 1, 2, 3} have weight 7?

According to the general equation for conditional probability if p(anb)=3/7 and p(b)=7/8 what is p(a i b)

Jeremy wants to determine the number of solutions for the equation below without actually solving the equation. which method should jeremy use?

Thomas is using a drawing program to complete a construction. which construction could he be completing? two perpendicular lines are drawn. inscribing an equilateral triangle in a circle inscribing a square in a circle inscribing a regular pentagon in a circle inscribing a regular hexagon in a circle