Answer:
a positive even number.
Step-by-step explanation:
I suggest plugging in random positive even numbers and finding a pattern. (-12)^2 = 144. (-12)^ 4= 20,736. this is because two negatives, when multiplied, turn to a positive. the n is how many times negative 12 is multiplied with itself
a:b = 6:10 = 3:5 = 21:35
b:c = 21:33 = 7:11 = 35:55
a:b:c = 21:35:55
