$\displaystyle {f{{\left({x}\right)}}}={\left\lbrace\begin{array}{c} {x}^{{2}}+{1}{\quad\text{if}\quad}\text{x <= 1}\\{3}\cdot{x}+{C}{\quad\text{if}\quad}{x}>{1}\end{array}\right.}$

What value of C will make this function continuous at x = 1?

$\displaystyle {C}=$

(Hint: For a function to be continuous at x=a, the left limit must equal the right limit as x->a.)