what amount invested today at 6% compounded monthly will support perpetual monthly payment of 500? the first payment will be made one month from now

I’m stuck on this i don’t understand.

Ablock of wood is a cube whose side is x in. long. you cut off a 1-inch thick piece from the entire right side. then you cut off a 3-inch thick piece from the entire top of the remaining shape. the volume of the remaining block is 2,002 in3. what are the dimensions of the original block of wood?

Isee the amount was $90.00 then reduced to $75.00 , what is the percent ?