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Answer:
(b) y = -5x
Explanation:
When "y varies directly as x" the equation for that is ...
y = kx . . . . . . . for some constant k
The value of k can be found by solving for it:
k = y/x . . . . . . divide by x
So, the given point (x, y) = (2, -10) tells you the value of k is ...
k = -10/2 = -5
and the direct variation equation is ...
y = -5x
_____
Additional comments
There are a couple of other useful facts about direct variation. When you compare the equation to the slope-intercept form equation for a line, ...
y = mx + b
you see that b=0 and the slope, or rate of change, (m) is the same as k.
The y-intercept of 0 means that the graph of any direct-variation equation must go through the origin. (If it does not, then the variation is not direct.)