Set 13: Linear Equations

Choice C is correct. Choice C is the correct answer. We add to undo the subtraction. 1. Start with the equation: $x - 40 = 25$ 2. Add 40 to both sides: $x = 25 + 40$ 3. Calculate: $x = 65$ 4. Verify: $65- 40 = 25$ ✓ The pattern holds regardless of the size of the numbers: addition is always the inverse of subtraction. Choice A is incorrect because this results from subtracting instead of adding: $25- 40 = -15$. This applies subtraction twice. Choice B is incorrect because this is the absolute value of Choice A, perhaps from dropping the negative sign: $|{-15}| = 15$. Choice D is incorrect because this results from dividing: $\frac{25}{40} = 0.625$. Division is not the inverse of subtraction.