Final answer:
The equation that represents the direct variation relationship where a varies directly is y = (7/2)x.
Step-by-step explanation:
The equation that represents the direct variation relationship where 'a' varies directly is in the form y = kx.
In this case, we are given that a = 7 when b = 2. To find the equation, we need to determine the value of k, which is the constant of variation. To do this, we will set up a proportion using the given values: a/b = k.
Plugging in the given values, we have 7/2 = k. Therefore, the equation that represents the direct variation relationship is y = (7/2)x.