Numerical Methods: Euler to Runge–Kutta · Easy problem

Apply one step of the improved Euler (Heun) method with $h = \dfrac{1}{2}$ to $y' = 2t$, $y(1) = 4$. Heun's step is $y_1 = y_0 + \dfrac{h}{2}\left(k_1 + k_2\right)$ with $k_1 = f(t_0, y_0)$ and $k_2 = f(t_0 + h,\ y_0 + h k_1)$. What is the estimate of $y\left(\dfrac{3}{2}\right)$? Express your answer as a common fraction.