What do these mean? They are supposed to represent things but I don't understand them. C=2╥r for r,
S=P+Prt for t,
and A=2lw+2lh+2wh for h
C is the circumference of a circle with radius r
S is the ending account balance after t periods of simple interest at "r%"
A is the surface area of a w x l x h rectangular solid (like a brick)