Question 690699
Area = length x width
First convert cm to m
( cm ) x ( 1 m / 100 cm ) = m 
{{{ 400 * ( 1/100 ) = 4 }}} m
{{{ A = L * 400 }}}
{{{ 12 = L * 4 }}}
{{{ L = 12/4 }}}
{{{ L = 3 }}}
The length is 3 m