Answer:
b = 6
Explanation:
To find the answer, find the GCF of 7 and 21, which is 7, and divide it by 7/7 to get 1/3, now the equation is 1/3 = b/18. How many times does 3 multiply to get 18? 6, multiply the first side of the equation by 6/6 to get 6/18, now we have 6/18 = b/18, since they are the same, b = 6