Correct Answer: A

Rationale: To solve the equation 3x - 5 = 10, start by isolating x. Add 5 to both sides of the equation to get 3x = 15. Then, divide by 3 on both sides to find x = 5. Therefore, the correct answer is x = 5. Choice B, x = 10, is incorrect because adding 5 to 10 does not yield 10. Choice C, x = 15, is incorrect as adding 5 to 15 does not equal 10. Choice D, x = 20, is incorrect because adding 5 to 20 does not result in 10.

Correct Answer: A

Rationale: To add fractions, find a common denominator, which in this case is 40. Convert each fraction to have the common denominator: 7/8 = 35/40, 9/10 = 36/40, and 6/5 = 48/40. Add these fractions to get 119/40. Simplify this improper fraction to a mixed number, which is 3 & 39/40. Choice B and C are incorrect as they do not represent the sum of the fractions. Choice D is incorrect; the whole number part should be 3, not 2.

Correct Answer: C

Rationale: Rationale: To find the least common multiple (LCM) of 14 and 21, we need to determine the smallest number that is a multiple of both 14 and 21. First, list the multiples of 14: 14, 28, 42, 56, 70, 84, ... Next, list the multiples of 21: 21, 42, 63, 84, ... The smallest number that appears in both lists is 42. Therefore, the LCM of 14 and 21 is 42.

Correct Answer: B

Rationale: 1/4 gram is equivalent to 1/4 * 1000 milligrams (since 1 gram = 1000 milligrams). 1/4 * 1000 = 250 milligrams. Therefore, the equivalent dosage in milligrams is 250mg, which corresponds to option B. The other choices are incorrect because they do not correctly convert 1/4 gram to milligrams using the conversion factor of 1 gram = 1000 milligrams.

Correct Answer: A

Rationale: To find the value of x, set up the proportion 7/9 = x/63. Cross multiply to get 7*63 = 9*x. This simplifies to 441 = 9x. Divide both sides by 9 to solve for x, giving x = 49. Therefore, the correct answer is A. Choice B (x = 39), Choice C (x = 50), and Choice D (x = 59) are incorrect as they do not match the correct calculation based on the proportion set up.