First one
y = 5x
Let x = 2a
y = 5(2a) = 10a
When x doubles we have
y = 5(4a) = 20a
So....when x doubles y doubles ⇒ "A"
Second one
y =5/x
Let x = 2a
y = 5 / (2a) = (1/2)*5a
Now....let x triple and we have that
y = 5 / (6a) = (1/6) * 5a
So....when x triples, y is 1/3 of its original value ⇒ "D"
