Having trouble with if(x=y,z,a) formula

I'm not sure if I can even do this as a formula and if I would have to create a macro for this but I was hoping someone could help me figure out what the formula would be to accomplish my task. Here and overview.

What I have is budget that I’m trying to create with accounts that will work interactively with each other.
I’m trying to do this: Account 1: 150 Cell(A1)
Account 2: 150 Cell(A2)
Account 3: 200 Cell(A3)
Excess of Acct. 3: x Cell(A4)
if x>=0 then Account 2 = 150 If account
If x<= 150 then Account 2 =0 and excess of that is subtracted from Account 3
Other wise Account 2 - Excess of account 3

Written out: If I spend more than 200 dollars from account 3 then that goes into excess of account 3 which lowers the budget of of Account 2 and account 1. So if there is no excess from account 3 then Account 2 will equal 150 dollars. If there is an excess from account 3 and it is less than 150 dollars then I want the excess to be subtracted from Account 2 in cell A2. So lets say excess is 100 then Account 2 should equal 50 dollars. If excess is great than 150 then I want Account 2 to equal zero and the excess of that subtracted from account 1 in Cell (A1). So if excess is 200 then subtract account 2 in (A2) will be zero and account 1 in cell (A1) will equal 100.


I was trying to use the if(x=y,z,a) formula but I wasn't clever enough to get it to work... I'm sorry if I over explained it and I apprecaite any help in the matter.

Thanks in advance,

Moe

Assuming:

A5: Amount spent (you enter in this cell the amount of money you spent)

A1: =IF($A$5>350, MAX(0, 550-$A$5), 150)
A2: =IF($A$5>200, MAX(0, 350-$A$5), 150)
A3: =MAX(0, 200-A5)