Centripetal force to the revolving planet around sun is provided by gravitational force.
where G is gravitatationalconstant, M is mass of sun , m is mass of planet,
R is mean distance between sun and planet and ω is angular speed of revolution
and T is period of revolution around sun.
from eqn.(1), we can write
RV and RE are mean distances from sun for Venus and Earth respectively
RM is mean distance of Mars from sun