Question

"two planets have the same mass, but planet a has 3 times the radius of planet

Answer 1

The gravitational acceleration on the surface of planet A is:
$g_A = \frac{GM_A}{r_A^2}$
where G is the gravitational constant, $M_A$ is the mass of planet A and $r_A$ its radius.

Similarly, the gravitational acceleration on the surface of planet B is:
$g_B = \frac{GM_B}{r_B^2}$

The ratio between the gravitational acceleration on planet A and B becomes:
$\frac{g_A}{g_B}= \frac{GM_A / r_A^2}{GM_B/r_B^2} = \frac{M_A r_B^2}{M_B r_A^2}$

The problem says that the two masses are equal: $M_A = M_B$ while planet A has 3 times the radius of planet B: $r_A = 3 r_B$. Substituting into the ratio, we get:
$\frac{g_A}{g_B} = \frac{M_B r_B^2}{M_B (3 r_B)^2} = \frac{1}{9}$

so, gravity on planet B is 9 times stronger than planet A.