EXAMPLE 1 RESULT: $\overline{t}=12,9\text{µm}$

The dash should not be that far from 't' and a random spacing was added. How it should be:

EXAMPLE 2 RESULT: ${\lambda }_{\text{C}}=\frac{d}{\sqrt{D{e}_{\text{c}}}}\le 10$

The square root is merged into upper part. How it should be: