$28=\boxed{4}\cdot \boxed{7}$

$30=\boxed{5}\cdot \boxed{6}$

$32=\boxed{4}\cdot \boxed{8}$

$35=\boxed{5}\cdot \boxed{7}$

---

$36=\boxed{6}\cdot \boxed{6}$    lub    $36=\boxed{4}\cdot \boxed{9}$

$40=\boxed{5}\cdot \boxed{8}$

$42=\boxed{6}\cdot \boxed{7}$

$45=\boxed{5}\cdot \boxed{9}$

---

$48=\boxed{6}\cdot \boxed{8}$

$49=\boxed{7}\cdot \boxed{7}$

$54=\boxed{6}\cdot \boxed{9}$

$56=\boxed{7}\cdot \boxed{8}$

---

$63=\boxed{7}\cdot \boxed{9}$

$64=\boxed{8}\cdot \boxed{8}$

$72=\boxed{8}\cdot \boxed{9}$

$81=\boxed{9}\cdot \boxed{9}$