Question 700160
Think of one plane as being stationary and
the other plane approaching at the sum of their speeds.
Let {{{ s }}} = the speed of the slower plane
{{{ s + 55 }}} = the speed of the faster plane 
{{{ 3260 = ( s + s + 55 )*4 }}}
{{{ 3260 = ( 2s + 55 )*4 }}}
{{{ 3260 = 8s + 220 }}}
{{{ 8s = 3040 }}}
{{{ s = 380 }}}
{{{ s + 55 = 435 }}}
Their speeds are 380 mi/hr and 435 mi/hr
check:
{{{ 380*4 = 1520 }}} mi
{{{ 435*4 = 1740 }}} mi
{{{ 1520 + 1740 = 3260 }}} mi
OK