Question 490162
Write an equation for each
The liner:
{{{ d[1] = r*t }}}
{{{ d[1] = 30t }}}
The helicopter:
{{{ d[2] = r*t }}}
{{{ d[2] = 66t }}}
-------------
Wait until the helicopter leaves the port,
and start a stopwatch. Also, figure out how much 
of a head start the liner got
{{{ d[hs] = 30*3 }}} (3 hrs)
{{{ d[hs] = 90 }}} km
------------
Both will travel for the same amount of time, but
the liner will travel {{{ 90 }}} km less distance
(1) {{{ d[2] = 66t }}}
(2) {{{ d[2] - 90 = 30t }}}
This is 2 equations and 2 unknowns, so it's solvable
Substitute (1) into (2)
(2) {{{ 66t - 90 = 30t }}}
(2) {{{ 36t = 90 }}}
(2) {{{ t = 2.5 }}} hrs
This is the time elapsed from when the 
helicopter leaves at 10 am, so it catches up
with the line at 12:30
check answer:
(1) {{{ d[2] = 66t }}}
(1) {{{ d[2] = 66*2.5
(1) {{{ d[2] = 165 }}}
and
(2) {{{ d[2] - 90 = 30t }}}
(2) {{{ d[2] - 90 = 30*2.5 }}}
(2) {{{ d[2] = 90 + 75 }}}
(2) {{{ d[2] = 165 }}}
OK