Answer: I am not to sure but I believe that the correct answer is 21
Step-by-step explanation: I believe this is the correct answer because on the number line the numbers generally follow a sequenced order beginning with the lowest number and increasing towards larger numbers. The lowest number in this question is 21 and in the American systems we read left to right causing the number line to begin with the lowest number from the left and going to the right. The order would be 21, 48, 53, 64, 95.