How can I convert this if statement to an arrow function?

I have an function with an if statement that says:

function reflect() {
    if (number_a >= 600) {
         ball_velocity_a = -ball_velocity_a }
    if (number_b >= 600) {
         ball_velocity_b = -ball_velocity_b
}}

and I'm trying to convert this function into arrow function

const deflect = () => number_a >= 600 ? ball_velocity_a = -ball_velocity_a : 

but I'm not sure what to put after the : as ball_velocity_b is conditioned with number_b instead of number_a. I'm really new to arrow functions and would appreciate some help on this.