The three pairs of corresponding angles have the same measures, so the triangles are similar by AA similarity. However, at least one pair of corresponding sides must be shown congruent before the triangles can be declared congruent.
There is nothing in the diagram to require the triangles be congruent.
In order to calculate interest receivable and interest revenue for notes receivable, you can multiply the interest rate by the amount of notes receivable and then divide by 12 to capture the monthly rate.
