<u>Answer:</u>
<em>1. The equations are </em>
<em>2. we can use elimination method to solve the problem</em>
<em>3. She has 50 5$ bills and 30 10 $ bills</em>
<em>4. The values of x and y that we found satisfies the two equations which ensures that the solution is correct.</em>
<em>5. Elimination method involves lesser number of steps when compared with graphical method and substitution method.</em>
<u>Explanation:</u>
<em>Number of 5$ bills=x</em>
<em>Number of 10$ bills=y</em>
<em>Total number of bills=80</em>
<em>total amount=$550</em>
Here we have two equations and we can use elimination method to solve the set of equations
<em> (Equation 1)</em>
<em> (Equation 2)</em>
<em>We have to make the coefficient of one variable in both equations same.</em>
<em>Let us make the coefficient of x same.</em>
<em> (Equation 3)</em>
<em>Subtract (3)from (2)</em>
<em></em>
<em></em>
<em></em>
<em></em>
<em>Substitute the value of y in equation (1)</em>
<em></em>
<em></em>
<em></em>
<em></em>
<em>x=50</em>
<em>y=30</em>