$(7.9\%$ of $134) - (3.4\%$ of $79) = $x$

### Concept & Formula This problem can be drastically simplified by using algebraic factoring rather than brute-force calculation. The key is to find common numerical elements to pull out. $$ \text{Value} = \frac{P}{100} \times N $$ ### Step-by-Step Solution * **Given:** $(7.9\% \text{ of } 134) - (3.4\% \text{ of } 79)$ * **Calculation:** Express both terms as decimals. $$ (0.079 \times 134) - (0.034 \times 79) $$ * Notice the relationship between $0.079$ and $79$. We can rewrite $0.034 \times 79$ by shifting decimals to match the $7.9$ pattern. $$ 0.034 \times 79 = 0.34 \times 7.9 $$ * Also, write the first term using $7.9$. $$ 0.079 \times 134 = 7.9 \times 1.34 $$ * Substitute these back into the expression. $$ (7.9 \times 1.34) - (7.9 \times 0.34) $$ * Factor out the common $7.9$. $$ 7.9 \times (1.34 - 0.34) $$ $$ = 7.9 \times 1.00 $$ $$ = 7.9 $$ * The value $7.9$ is not among the specific numeric options (a, b, c, d). ### Exam Strategy & Shortcut The factoring method demonstrated above is the ultimate shortcut. Spotting that $7.9 \times 134$ and $3.4 \times 79$ share the base digits '79' allows you to completely avoid three-digit decimal multiplication. $7.9 \times (1.34 - 0.34) = 7.9$ can be solved mentally in under 10 seconds. ### Common Pitfall Manually calculating $0.079 \times 134 = 10.586$ and $0.034 \times 79 = 2.686$. While this will eventually lead to the correct answer of $7.9$, the heavy decimal arithmetic is a massive time drain and prone to carrying errors. ### Final Answer **Therefore, the correct answer is None of these.**