Felix is purchasing a brownstone townhouse for ​$2,500,000. To obtain the​ mortgage, Felix is required to make a 18​% down payment. Felix obtains a 30​-year mortgage with an interest rate of 7.5​%.

To find out the amount of the down payment, we first need to calculate 18% of the total purchase price:

Down payment = 0.18 * $2,500,000
Down payment = $450,000

Now, we need to calculate the loan amount Felix will need:

Loan amount = Total purchase price - Down payment
Loan amount = $2,500,000 - $450,000
Loan amount = $2,050,000

Next, we need to calculate Felix's monthly mortgage payments using the loan amount and interest rate. We can use the formula for a fixed-rate mortgage:

M = P[r(1+r)^n]/[(1+r)^n-1]

Where:
M = monthly mortgage payment
P = loan amount ($2,050,000)
r = monthly interest rate (annual rate divided by 12 months)
n = number of payments (30 years * 12 months)

r = 7.5 / 100 / 12
r = 0.00625

n = 30 * 12
n = 360

M = $2,050,000[0.00625(1+0.00625)^360]/[(1+0.00625)^360-1]
M = $14,335.51

Therefore, Felix's monthly mortgage payment will be $14,335.51.