If the average sunflower has 34 petals, to best estimate the total number of petals on 57 flowers, we can multiply the average number of petals on each flower, 34, by the total number of flowers we have to find the petals for, 57.
Doing 34 * 57 gives us 1938, so the best estimate of the total number of petals on 57 sunflowers is 1938.