Question

'if I borrowed 1380 for 15 months at 13%APR what will be her monthly payment

Answer 1

I will assume you are using compound interest and the monthly rate is .13/12 or
i = .0108333...
n = 15
payment = p

p( 1 - 1..0108333..^-15)/.0108333... = 1380

I get p = 100.17