Ineed to know equation before can solve it . i don't know what is equation . pls

Assume the number is x 
two twice the number is 2*x = 2x 
and the difference between (two twice the number ) and ( 5 ) = (8) 
so , 2x -5 = 8 and this is the equation 
to get the x value from the equation we need to eliminate the (-5) 
so add (+5) to the both sides ,, 2x -5 +5 = 8+5 
so, 2x= 13 
x= 13/2 

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