Given:

• Width = $\frac{4}{5}b\backslash frac\{4\}\{5\}b$
• Length = $\frac{5}{4}b+20\backslash frac\{5\}\{4\}b\; +\; 20$

The area $AA$A of the rectangle is calculated as: $A=Width\times Length=\left(\frac{4}{5}b\right)\times (\frac{5}{4}b+20)A\; =\; \backslash text\{Width\}\; \backslash times\; \backslash text\{Length\}\; =\; \backslash left(\backslash frac\{4\}\{5\}b\backslash right)\; \backslash times\; \backslash left(\backslash frac\{5\}\{4\}b\; +\; 20\backslash right)$

A=Width×Length

 Now, distribute $\frac{4}{5}b\backslash frac\{4\}\{5\}b$ across the terms inside the parentheses: $A=\frac{4}{5}b\cdot \frac{5}{4}b+\frac{4}{5}b\cdot 20A\; =\; \backslash frac\{4\}\{5\}b\; \backslash cdot\; \backslash frac\{5\}\{4\}b\; +\; \backslash frac\{4\}\{5\}b\; \backslash cdot\; 20$

1. $\frac{4}{5}b\cdot \frac{5}{4}b=b^2\backslash frac\{4\}\{5\}b\; \backslash cdot\; \backslash frac\{5\}\{4\}b\; =\; b^2$
2. $\frac{4}{5}b\cdot 20=16b\backslash frac\{4\}\{5\}b\; \backslash cdot\; 20\; =\; 16b$

So, the area is: $A=b^2+16b$ The answer is: $A=b^2+\mathrm{16b}square\; feet$