Returns to Scale off a figure

This is the table given for levels of output for different levels of inputs.

$$\begin{pmatrix} Q & K & L\\ 100 & 3 & 6\\ 200 & 5 & 10\\ 300 & 7.5 & 15 \\ 400 & 10 & 20 \\ 500 & 12.5 & 25 \\ 600 & 15 & 30 \end{pmatrix}$$

These are questions on my Final review guide and I am getting different answers than my professor and feel like he may be wrong. Here are the questions.

1) Which of the following conclusions can be drawn from this information?

• A)Increasing returns to scale exist between 100 and 200 units of output.

• B) Constant returns to scale exist throughout all levels of production.
• C) Labor is subject to diminishing marginal productivity in the short run.

• D) No firm conclusions can be drawn.

2)Returns to scale are greatest at which level of output?

• A) 100-200 units

• B) 200-400 units

• C) 400-600 units

• D) There is insufficient information to answer the question.

3) At which level of input are there constant returns to scale?

• A) 400-600 units

• B) Constant returns to scale exist throughout all levels of production.

• C) Constant returns to scale do not exist at any level of production.

• D) No firm conclusions can be drawn.

The Answers I concluded were 1) D, 2) C, and 3) C

I can give you my professor's answers if need be. But if what you guys respond with is the same as what my professor has then I will contact him.

• Do you know how to determine increasing, constant, and decreasing returns to scale in general? – Herr K. May 2 at 19:23
• Yes I do, at first, it made it hard because there is no equation but after looking at it farther I understand now why I am wrong. – Displayer124 May 2 at 20:06