At 24C, an insect takes 15 hours to hatch from the egg stage…

At 24C, an insect takes 15 hours to hatch from the egg stage and 21 hours to complete the first instar. Using 10C as a threshold, what is the total number of degree hours it takes this insect to reach the second instar (i.e., complete the first instar)? List only the number itself in your answer.