I am really struggling with these 2 questions. Please help!

1)Mars has a mass of about 6.91 × 1023 kg,
and its moon Phobos has a mass of about
9.8 × 1015 kg.
If the magnitude of the gravitational force
between the two bodies is 4.87 × 1015 N,
how far apart are Mars and Phobos? The
value of the universal gravitational constant
is 6.673 × 10−11 N · m2/kg2.
Answer in units of m. (2.11336211e-5m)
2) (Only part B)
a-Objects with masses of 195 kg and 734 kg
are separated by 0.379 m. A 21.1 kg mass is
placed midway between them.

Find the magnitude of the net gravitational
force exerted by the two larger masses on the
21.1 kg mass. The value of the universal gravi-
tational constant is 6.672 × 10−11 N · m2/kg2.
Answer in units of N.

b-Leaving the distance between the 195 kg and
the 734 kg masses fixed, at what distance from
the 734 kg mass (other than infinitely remote
ones) does the 21.1 kg mass experience a net
force of zero?
Answer in units of m.

1 answer

the first

f=GM1M2/d^2
you have all, so find d.

the scond

draw the figure on a scale, the distance then from mass1 to the 21kg is x, the distance to mass2 is d-x, where d is the distance in the first problem.

set the two forces equal, and solve for x