For the example A (SFH, simplest case), roughly,
cap rate = (annual cash flow - annual rent * 0.05) / cash down
= 12 * (400 - 1800*0.05) / 37750
= 9.854%
Note: The parameter 0.05 means that 5% of your rent will be lost for vacancy and repairs (during and after rent). I would use larger number like 7% for this.