BECE Mathematics 2022 Paper

Let $x$ be the numberA certain number $(x)$ is subtracted from $12 \rightarrow$ result $=12-x$The result is multiplied by $3 \rightarrow (12-x) \times 3$The answer is $21 \rightarrow (12-x) \times 3 = 21$Now solve for $x$$\; (12-x) \times 3 = 21$$\; a(b-c) = a \times b - a \times c$$\; (12-x) \times 3 = 12 \times 3 - 3 \times x$$\; 12 \times 3 - 3 \times x = 36 - 3x$$\; 36 - 3x = 21$ Move the $-3x$ to the right side of the equation and 21 to the left- $3x$ becomes $3x$ at the right (when negative crosses the equal to sign becomes positive21 becomes -21 at the left$\; 36 - 21 = 3x$$\; 15 = 3x$Divide both sides of the equation by 3 to make $x$ the subject$\; \frac{15}{3} = \frac{3x}{3}$$\; 5 = x$$\; \therefore x = 5$You can verify$\; 12 - 5 = 7 \; \text{(Result)} \;$$\; 7 \times 3 = 21 \; \text{(Answer)} \;$