To find the area of the base \( B \) of a rectangular prism, you can use the formula:
\[ B = \text{length} \times \text{width} \]
First, we need to convert the mixed numbers for the length and width into improper fractions.
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Convert the length \( 7 \frac{1}{4} \) m: \[ 7 \frac{1}{4} = 7 \times 4 + 1 = 28 + 1 = 29 \quad \text{(improper fraction: } \frac{29}{4}\text{)} \]
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Convert the width \( 10 \frac{1}{2} \) m: \[ 10 \frac{1}{2} = 10 \times 2 + 1 = 20 + 1 = 21 \quad \text{(improper fraction: } \frac{21}{2}\text{)} \]
Now, substitute the improper fractions into the area formula:
\[ B = \frac{29}{4} \times \frac{21}{2} \]
To multiply the fractions, multiply the numerators and the denominators:
\[ B = \frac{29 \times 21}{4 \times 2} = \frac{609}{8} \]
Now, convert \( \frac{609}{8} \) into a mixed number.
- Divide 609 by 8:
\[ \text{609 divided by 8} = 76 \quad \text{(since } 76 \times 8 = 608\text{)} \]
- The remainder is \( 609 - 608 = 1 \).
Thus, we have:
\[ \frac{609}{8} = 76 \frac{1}{8} \]
Therefore, the area of the base \( B \) of the rectangular prism is:
\[ \boxed{76 \frac{1}{8}} \quad \text{m}^2 \]