Answer:
Step-by-step explanation:
It looks like every time the coefficient increases by 3 while the exponent increases by 1.
[tex]\\45\\\sum 3(n+1)x^{n}\\n = 0[/tex]
Notice it starts at zero so 3 is multiplied by (x+1) to make it start from 0
The exponent is simply n, because at the start is it zero [tex]x^0=1[/tex], then 1, then 2, so on.
The upper limit is 45 because 45 - 0 = 45 terms
