Definite Integrals and Function Symmetry

Let $t$ be a function that satisfies the property $t(-x) = -t(x)$ for all real numbers $x$. If $\displaystyle\int_1^3 (t(x) + x^2)\,dx = 18$, what is the value of $\displaystyle\int_{-3}^{-1} (t(x) + x^2)\,dx$?