Answer: C) 3*15 = 9*x
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Step-by-step explanation:
Anything in the form A/B = C/D will cross multiply to A*D = B*C
In this case, A = 3, B = 9, C = x and D = 15
So that's why 3/9 = x/15 cross multiplies to 3*15 = 9*x
Check out the diagram below for more information.