CAT 2019 Coordinate Geometry — Previous Year Question

Let C be a circle of radius $\sqrt{20}$ cm. Let L1, L2 be the lines given by $2x - y - 1 = 0$ and $x + 2y - 18 = 0$, respectively. Suppose that L1 passes through the center of C and that L2 is tangent to C at the point of intersection of L1 and L2. If $(a,b)$ is the center of C, which of the following is a possible value of $a + b$?