You have the following sequence:
f(n) = 2n + 3
In order to calculate which is the 40th term of the previous sequence, you take into account that the 40th term coincides with a value of n = 40.
Then, you simply replace the value of n into the sequence f(n), and operate, just as follow:
40th term of the following sequence:
f(n) = 2n + 3 replace n by 40
f(40) = 2(40) + 3 coefficients besides the value of n means a multiplication
f(40) = 80 + 3 simplify
f(40) = 83
Hence, the 40th term of the given sequence is number 83, that is, the second option