Question 846795
Part (a):

The delivery truck drives in one direction on a pathway and the shop owners drive in the opposite direction.  Sum of the distances traveled would be 90 km.  MEET after {{{1/2}}} hour.


Vehicle________speed_______time___________distance
Truck___________r__________1/2____________r(1/2)
Tam&Michael____r+20________1/2____________(r+20)(1/2)
Total_____________________________________90


Find truck speed.
{{{highlight_green(r/2+(r+20)/2=90)}}}------based on the total distances each travel
{{{r+r+20=180}}}
{{{2r+20=180}}}
{{{2r=160}}}
{{{highlight(r=80)}}} km per hour
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Meeting happens 40 km from the warehouse.
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That was for part (a).  It ONLY USES one equation to solve the the unknown variable r.  You would then simply use R*T=D (Rate, Time, Distance) to find the distances; in this case, the distance from the warehouse where the owners meet the truck, which is simple {{{80*(km/hour)*(1/2)*hour=highlight(40*km)}}}.
You can also easily get the speed of Tamara & Michael, because if they move 20 km/hour faster than the truck, then their speed is {{{80+20=highlight(100)}}}.


Part (b)  is too open-ended.  Is it supposed to be so?  Does it have some further constraining information given?  TOO, too, openended.
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NEW THOUGHT:
Maybe this part need not be so open-ended.  ASSUMING the truck would leave its warehouse in time to be 40 km from warehouse at a time a little before 7:30AM, then Tamara and Michael could make that distance in the half-hour specified for part (a). their round-trip to pickup the coffee beans would allow them to be able to return by 8:30AM with their supply of beans.