$($a$)$ Two microwave frequencies are authorized for use in microwave ovens, $890$ and $2555$ MHz $.$ Calculate the wavelength $($in cm $)$ of each.

cm$\}(\backslash$mathrm$\{$ frequency $=890$ MHz$)$

cm$\}\backslash$mathrm$\{($frequency $=2555$ MHz$)$

$($b$)$ Which frequency $($in MHz $)$ would produce smaller hot spots in foods due to interference effects?

$MHz$