${}_{\text{m}\text{a}\text{t}}=\frac{4t_{\text{m}\text{a}\text{t}}}{D}$

$k_{\text{m}\text{a}\text{t}}=0\mathrm{.}217({}_{\text{m}\text{a}\text{t}}\frac{f_{c\text{m}\text{a}\text{t}}}{f_{c0}}{)}^{\frac{3}{2}}$

$f_l=\frac{2E_f{}_f{t}_f{n}_f}{D}$

$f_{t\text{m}\text{a}\text{t}}=0\mathrm{.}1f_{c\text{m}\text{a}\text{t}}$

$f_{lm}=\frac{2f_{t\text{m}\text{a}\text{t}}{t}_{\text{m}\text{a}\text{t}}}{D}$

$\frac{f_{cc}}{f_{c0}}=1+0\mathrm{.}21(\frac{f_{lm}}{f_{c0}}{)}^{\frac{1}{3}}+4\mathrm{.}81k_{\text{m}\text{a}\text{t}}(\frac{f_l}{f_{c0}}{)}^{\frac{2}{3}}$

Explain the equation and how it is derived.