first thing to find the average acceleration is to figure out what the increase in speed was, we can do that by subtracting the original speed from the speed after accelerating, that looks like:
40 - 12 = 28
so the lizard accelerated 28 m/s in 6 seconds, to find the average increase in m/s every second, we divide the m/s by the seconds, which gives us:
Rainbows are caused by the dispersion of light, which itself consists of a combination of refraction and reflection of light around little droplets of water.