Newb: Simple Explicit Formula

[Duplicitous]

I am incredibly new to python (I'm officially on my fourth day of learning) and as a test of what I've learned so far, I wanted to make a simple Explicit Formula calculator. The formula is:

a(n) = a(1) + (n - 1)d

This is what I came up with:

aone = raw_input("Enter the first term: ")
n = raw_input("Enter the n term: ")
d = raw_input("Enter the difference: ")

answer = n - 1
answer = answer * d
answer = answer + aone

print answer

The printout from the terminal is this: 

Output:
python expForm.py
Enter the first term: 2
Enter the n term: 100
Enter the difference: 5
Traceback (most recent call last):
  File "expForm.py", line 5, in <module>
    answer = eval('aone + (nterm - 1) * diff')
  File "<string>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'str' and 'int'

I'm sorry if I look like the biggest imbecile on the planet, but this is beyond me at this stage in my coding abilities. Sorry. :(