Will someone tell how you would solve this equations?

Question

solve for p:
r=mp-p

2z-(1-z)=11z

Answer 1

1: r=p(m-1)
p=r/(m-1)

2: 2z-(1-z)=11z
2z-1-z=11z
z-1=11z
z-11z=1
z(1-11)=1
z=(-1/10)

Answer 2

for mp-p you need to change it into p(m-1)
that gives you r=p(m-1)
then you r/(m-1)=p

Subtrat 2z from both sides leaving you with -(1-z)=9z
multiply -(1-z) to get -1+z
That leaves you with -1+z=9z
subtract z from both sides hence -1=8z
z=-1/8

Answer 3

r=p(m-1)
p= r/(m-1)

2z-1+z=11z
3z-1=11z
11z-3z=-1
z(11-3)=-1
z=-1/8

Answer 4

the first one is three variables in one equation. for that u require two more equations.

second one has already been solved.