MHB V.02.Binary operator by a*b=a+8b

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karush
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Define the binary operator * by:
$a*b=a+8b$
Find each of the following

(the only thing I knew to do here was plug in)
[a.] $3*5\quad =3+8(5)=3+40=43$
[b.] $7*7\quad =7+8(7)=7+56=83$
[c.] $5*3\quad =5+8(3)=5+24=29$
[d.] $x*z\quad =x+8z$
 
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$7+56=63\ne83$. The rest is correct.
 
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