Maths!!!

1. Give y = 1+x/1-x , find the value of x when y=5.
y=1+x/1-x
put y=5,it gives
5=1+x/1-x
5-5x=1+x
5-6x=1
-6x=-4
x=2/3
2. Given 1/u+1/v = 1/f , find the value of f when u=15 and v=30.
1/u+1/v = 1/f
put u=15 and v=30,it gives
1/15+1/30=1/f
2/30+1/30=1/f
3/30=1/f
1/10=1/f

1.
5=1 x/1-x
5-5x=1 x
5-1=x 5x
4=6x
1.5=x
x=1 1/2 or 1.5
-------------------------
2.
1/15 1/30=1/f
1/10=1/f
f=10