n is the term that you are looking for. it asked for the 3rd term so you replace n with 3. now its : 3 x 3^2 + 4 . you use the order of PEMDAS:
P arenthesis
E xponents
M ultipication
D ivision
A ddition
S ubtraction
you start with parenthesis but there are none so now exponents. 3^2 is 3 x 3. that would be: 3 x 3 = 9.
now multiplication. 3 x 9 + 4. 3 x 9 = 27
now division. there is none. so now addition and there is. 27 + 4 = 31.
then subtraction but there is none. so now you are done.
the 3rd term is therefore 31.
i hope that i helped.