Compare the proportional change in inputs to the proportional change in output at each step, since both factors are being scaled up together.

(a) Inputs double ($2\to4$); output rises from $10$ to $22$, a ratio of $2.2$ — greater than $2$. (b) Inputs double again ($4\to8$); output rises from $22$ to $40$, a ratio of $1.82$ — less than $2$.

Both labour and capital are doubled at each step, so the test is simply whether output MORE than doubles, EXACTLY doubles, or LESS than doubles.

1. From (2,2) to (4,4): inputs increase by a factor of $\dfrac{4}{2}=2$. Output increases by a factor of $\dfrac{22}{10}=2.2$. Since $2.2>2$, output has grown in a GREATER proportion than the inputs — this is Increasing Returns to Scale.
2. From (4,4) to (8,8): inputs again increase by a factor of $\dfrac{8}{4}=2$. Output increases by a factor of $\dfrac{40}{22}=1.82$. Since $1.82<2$, output has grown in a SMALLER proportion than the inputs — this is Diminishing Returns to Scale. This is a realistic pattern: the firm enjoys Increasing Returns to Scale while it is still small enough to benefit from greater specialisation and better use of indivisible factors, but as it grows very large, coordination difficulties set in and Diminishing Returns to Scale take over.
   ✓Final answer

   (a) Increasing Returns to Scale (output ratio $2.2>$ input ratio $2$). (b) Diminishing Returns to Scale (output ratio $1.82<$ input ratio $2$).

A common slip is comparing each row back to the FIRST row instead of to the IMMEDIATELY PRECEDING row — since the question asks about the returns to scale at each successive doubling, only the ratio between consecutive rows is relevant, not a comparison spanning multiple steps at once.