How much a parent pays in basic child support depends on the parents' incomes, how many children are in the household, and how old the child is. Those are the major factors. There are numerous other more minor factors.
You can get an estimate of what the basic child support is by using the free online child support calculator. The more accurate the information you input into the calculator, the more accurate the result will be. The calculator is at https://fortress.wa.gov/dshs/csips/ssgen .
The court may require that the parents provide their respective income tax returns and other documents with each other every year. However, unless the court orders the exchange there is no requirement that you share you pay information.
Parents will often argue what deductions, credits, and incomes are to be used in the calculation.
You run a risk that the court will not credit the payments you made to the mother if she claims you made no payment.
You should review the specific facts with your attorney to find out your legal options.