let radius;

let spacing = 15;

​

function setup() {

  createCanvas(400, 400);

  // how do we make NUM_CIRCLES evenly spaced circles?

  let circleSpace = width / NUM_CIRCLES;

  radius = circleSpace - spacing - (spacing/NUM_CIRCLES);

}

​

function draw() {

  background(220);

  for (let i = 0; i < NUM_CIRCLES; i+=1) {

    circle((radius/2) + spacing + i*(radius + spacing), 100, radius);

  }

}