Calculating an Equation in Excel

Hi, I'm trying to work out the answer to the following equation:

3500 - ((20000*(1.4-x))) - 0.1(20000*x) = 0

I wasn't able to work it out manually and so I tried to enter the equation into an Excel spreadsheet using the equation editor.

Using the equation editor, I managed to write down the equation easily enough but I wasn't able to action it.

I tried to use the autosum but with no joy. Please advise.

Hi, I've tried to execute your advice but I got the message that a formula had to be entered into cell A3.

So I put '=A2' into cell A3, and then went to 'goal seek' to 0 by changing A1, and it gave me the answer - 1.36111 - great.

However, if I enter x=1.36 into the equation, and calculate the result manually, I get an answer of -20. ??????????????