Answer:
[tex]51d=357\\\\d=\frac{357}{51} \\\\d=7[/tex]
Step-by-step explanation:
A proportion is an equation that defines that two ratios are equal. When the terms of a proportion are cross multiplied, the cross products are equal. Cross multiplication is the multiplication of the numerator of the first ratio by the denominator of the second ratio and the multiplication of the denominator of the first ratio by the numerator of the second ratio:
[tex]\frac{a}{b} =\frac{c}{d} \rightarrow ad=bc[/tex]
Therefore:
[tex]\frac{17}{d} =\frac{51}{21} \\\\17*21=d*51\\\\357=51d\\\\Solving\hspace{3} for\hspace{3} d\\\\d=\frac{357}{51} \\\\d=7[/tex]
