3 Answers

Kepler once said (T_E)^2 / (r_E)^3 = (T_M)^2 / (r_M)^3
E stands for Earth, M for Mars.
Substitute the info r_Mars = 1.53 * r_Earth.
(T_E)^2 / (r_E)^3 = (T_M)^2 / (1.53r_E)^3
Cancel r_E^3 from both fractions.
(T_E)^2 = (T_M)^2 / (1.53)^3
(T_M)^2 = 1.53^3 * (T_E)^2
Take the square root of both sides
T_M = 1.89 T_E = 1.89 years (duh)

1.52³/²= 1.87398 years.
it is the Sidereal year (in terms of stars) for Mars. Its synodal years is
1 – (1/1.87398) = 0.4663659 = 1/2.1441885,
or 2.1441885 years = 783 days … is the time between two consecutive oppositions.

Don’t you have a calculator?
1.52¹·⁵ = 1.873982
Even if you don’t have a calculator, there are ways to find square roots with a pencil and a piece of paper. You should find out how to do that. Most school kids learn the method in high school. Or, at least, they used to.