Question

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Answer 1

{$x=10$
{$3*10+5y=20$

{$x=10$
{$30+5y=20$

{$x=10$
{$5y=-10$

{$x=10$
{$y=-2$

The answer: (10;-2)

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Answer 2

Answer:  x = 10, y = -2 ;  → Write as:  (10, -2) .
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Explanation:
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Given:  
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              x = 10 ; 

        3x + 5y = 20 ;
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        → Plug in "10" for the value of "x" in the second equation:
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             3*(10) + 5y = 20 ;  Solve for "y" ;
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                       ↔   5y + 3*(10) = 20 ;  
 
             5y + 30 = 20 ;
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       Subtract "30" from EACH side of the equation:
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            5y + 30 − 30 = 20 − 30 ;
 
                       5y = - 10 ;
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  →  Divide EACH SIDE of the equation by "5" ; to isolate "y" on one side of the equation;  and to solve for "y" ;
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                       5y / 5  = - 10 / 5 ; 
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                         y  = - 2;  

And we are given:  x = 10 ;
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         → Let us check our answer, by substituting "10" for "x"; and "-2" for "y" ; in the second equation given; to see if the equation holds true:
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    Given: ...    3x + 5y = 20 ;

Substitute:     3*(10)  +  5*(-2)  = ?  20 ??  ;
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                         30  + (-10)  = ?  20 ?? ;
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                         30  − 10  = ? 20 ?  Yes;  "30 − 10 = 20 !!! " .
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                      So,  " x = 10 ,  y = -2 " ;  ↔ write as:  " (10, -2) " .
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