Apply $MRTS_{LK}=-\dfrac{\Delta K}{\Delta L}$ between each consecutive pair, since all five combinations lie on the same isoquant.

A→B: $\Delta K=-6\Rightarrow MRTS=6$. B→C: $\Delta K=-5\Rightarrow MRTS=5$. C→D: $\Delta K=-4\Rightarrow MRTS=4$. D→E: $\Delta K=-3\Rightarrow MRTS=3$.

$MRTS_{LK}=-\dfrac{\Delta K}{\Delta L}$, computed between each consecutive pair (each step has $\Delta L=1$):

A to B: $\Delta K = 14-20=-6$. $MRTS_{LK}=-\dfrac{-6}{1}=6$

B to C: $\Delta K = 9-14=-5$. $MRTS_{LK}=-\dfrac{-5}{1}=5$

C to D: $\Delta K = 5-9=-4$. $MRTS_{LK}=-\dfrac{-4}{1}=4$

D to E: $\Delta K = 2-5=-3$. $MRTS_{LK}=-\dfrac{-3}{1}=3$

The MRTS falls steadily — $6,5,4,3$ — confirming that this isoquant is convex to the origin, and that each additional unit of labour substitutes for progressively LESS capital than the unit before it, exactly as the Law of Diminishing Marginal Rate of Technical Substitution predicts.

Dividing $\Delta L$ by $\Delta K$ instead of $\Delta K$ by $\Delta L$ inverts the ratio entirely (giving, for example, $\dfrac{1}{6}$ instead of $6$ for the first step) — always keep capital given up in the numerator and labour gained in the denominator, since MRTS answers "how much capital per extra unit of labour," not the reverse.