a) 7.2 is 80% of 9
b) 16 is 4% of 400
Here, we want to solve the problems by writing an equation
a) Let x be the 80% of 9
Thus, we have it that;
[tex]\begin{gathered} \frac{80}{100}\times9\text{ = x} \\ \\ \frac{720}{100}\text{ = x} \\ \\ 100\times\text{ x = 720} \\ 100x\text{ = 720} \\ \text{ x = }\frac{720}{100} \\ x\text{ = 7.2} \end{gathered}[/tex]80% of 9 is 7.2
b) Let the percentage of 400 that is 16 be x
Thus, mathematically;
[tex]\begin{gathered} \frac{16}{400}\times100\text{ = x} \\ \\ 16\times100\text{ = 400}\times x \\ 1600\text{ = 400x} \\ x\text{ = }\frac{1600}{400} \\ x\text{ = 4\%} \end{gathered}[/tex]