Instead use WolframAlpha.com for math questions I would paste the answer but a cretinous fop has "disabled" that feature by javascript -- which is trivial to circumvent but I won't bother with the time.
Answer:
r = 1/6
Step-by-step explanation:

Multiply both sides by 4

Divide both sides by 3

Answer:
261.3cm3
Step-by-step explanation:
Answer: B) A=1/2(7)(12).
Explanation: The formula for area of a triangle is 1/2bh. Only B maintains this formula.