Using a proportional relationship, it is found that:
a) The equation is: y = 63/x.
b) When x = 21, the numeric value is of y = 3.
<h3>What is a proportional relationship?</h3>
A proportional relationship is a special case of a linear function, with slope represented by the constant of proportionality of k and intercept of 0.
When the two variables are inversely proportional, we have a inverse proportional relationship, in which the output variable y is obtained by the division of k by the input variable x, as follows:
y = k/x.
For this function, when y = 7, x = 9, hence the constant is obtained as follows:
7 = k/9
k = 9 x 7
k = 63.
Hence the equation is:
y = 63/x.
The numeric value of the function when x = 21 is given as follows:
y = 63/21 = 3.
More can be learned about proportional relationships at brainly.com/question/10424180
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