I'd like to know which of the following sentences are correct or sound more natural. The context is about the process of solving a maths problem:

a) Now the whole problem comes down to finding out the value of x

b) Now the whole problem comes down to find out the value of x

c) Now the whole problem boils down to finding out the value of x

d) Now the whole problem boils down to find out the value of x

e) Now the whole problem reduces to finding out the value of x

f) Now the whole problem reduces to find out the value of x

g) Now the whole problem is reduced to finding out the value of x

h) Now the whole problem is reduced to find out the value of x

Thank you very much.