Devaughn's age is two times sydney's age. the sum of their ages is
66. what is sydney's age?

D = devaugn's age
s = sidney's age

so, we know Devaugh's age is twice as Sydneys, so d = 2*s or 2s
and we know their sum is 66
or d + s = 66

since d = 2s, thus

(2s) + s = 66   <--- solve for "s" to see Sidney's age

what about Devaugn's?   well d = 2s

Graph a should be your answer