Help and explain how to solve these problems plz 10 points

It is given that y varies directly as x. If y = 5 when x = 4 determine the constant of variation.
A.-4/5\
B.4
C.5
B.5/4

It is given that y varies directly as x. If y = 10 when x = 3 determine the constant of variation.
A.-3/10
B.10
C.3
D.10/3

Which of these is true?

A.780,500 is less than 880,500.
B.780,500 is greater than 880,500.
C.880,500 is greater than 950,100.
D.880,500 is less than 780,500