Use ${\displaystyle \underset{a}{\overset{b}{}}}f(x)dx=\underset{n}{lim}{\displaystyle \underset{k=1}{\overset{n}{}}}f(c_k)x$ to evaluate the integral.

${\displaystyle \underset{1}{\overset{2}{}}}(4+3x^2)dx$

a$)39$

b$)33$

c$)13$

d$)11$