How would you write this in algebra

Which statement is not always true for a parallelogram? (a) opposite sides are congruent. (b) diagonals bisect each other. (c) it has 4 congruent angles. (d) consecutive angles are supplementary.

True or false look at the picture pls : /

If the tip varies directly with the number of guest which equation represents between the tip, t, and the number of guest, g?