Average speed is given by [Total Distance] ÷ [Total Time]
Average speed =

km/hour
9a - 3(a - 6) = -6...distribute thru the parenthesis
9a - 3a + 18 = -6....subtract 18 from both sides
9a - 3a = -6 - 18 ...combine like terms
6a = - 24...divide both sides by 6
a = -24/6
a = - 4
Take DEBC a parralelogram
Parralel sides are DE and BC
THEREFORE,
1/2*(a+b)*h
1/2*(6+15)*h
1/2*(21)*h=0
10.5*h=0
h=-10.5
Answer:36.5625
Step-by-step explanation:
Hope this helped!
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80-40/5-0=40/5=8 through the slope formula