Question 725185
Team B needs to go faster than a speed that will 
give them a tie right at the finish line
Team A has a head start of 
{{{ 7*(13/60) = 1.51667 }}}
Let {{{ t }}} = the time for them both to meet
at the finish line after B leaves 
Let {{{ s }}} = B's speed in mi/hr
--------------------------
A's equation:
(1) {{{ 77 - 1.51667 = 7t }}}
B's equation:
(2) {{{ 77 = s*t }}}
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(1) {{{ 7t = 75.48333 }}}
(1) {{{ t = 10.78333 }}}
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(2) {{{ s = 77/t }}}
(2) {{{ s = 77/10.78333 }}}
(2) {{{ s = 7.14065 }}}
Team B needs to go faster than 7.14065 mi/hr
check:
(1) {{{ 77 - 1.51667 = 7*10.78333 }}}
(1) {{{ 75.48333 = 75.48333 }}}
OK
(2) {{{ 77 = s*t }}}
(2) {{{ t = 77/ 7.14065 }}}
(2) {{{ t = 10.78333 }}}
OK