Question 1026237
Think of this as one of the buses standing still 
and the other one moving at the sum of their
speeds until they are 517.5 mi apart
{{{ 517.5 = ( 54 + 61 )*t }}}
{{{ 517.5 = 115t }}}
{{{ t = 517.5/115 }}}
{{{ t = 4.5 }}}
They will be 517.5 mi apart in 4.5 hrs
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check:
Slower bus:
{{{ d[1] = 54*4.5 }}}
{{{ d[1] = 243 }}} mi
and
{{{ d[2] = 61*4.5 }}}
{{{ d[2] = 274.5 }}}
and
{{{ d[1] + d[2] = 243 + 274.5 }}}
{{{ d[1] + d[2] = 517.5 }}}
which is correct -OK