Answer:
x=6
a=9
Step-by-step explanation:
Because 21 is 1.5 times 14, and 15 is 1.5 times 10, a has to be 1.5 times x. Also, x must be more than 4 in order for it to make a triangle. To make it simple, I'd use either 6 or 8. Just for ease, I'll use 6.
x=6
a=6*1.5=9
