Help with a mathematicial equation

I have a mathematicial problem.

I am supposed to get

Code:

---

b-x    x
---  = ---
 x    h-x

---

to become

Code:

---

    bh
x = ----
    b+h

---

I don't know the steps in the equation to get to there, so please show me that if you can. Also, what parts of mathematics would you recommend me to practice as I can't solve this?

this is just very elementary algebra...look at solution below: