Explanation
Step 1
Let
x represents the number of bills $1
y represents the number of bills $10
Luis has four times as many one-dollar bills as ten-dollar bills,then
[tex]x=4y\text{ Equation(1)}[/tex]Also,his total is still $43,then
[tex]\begin{gathered} 1\cdot x+10\cdot y=43 \\ x+10y=43\text{ Equation (2)} \end{gathered}[/tex]Step 2
find x and y , using Equation(1) and (2)
A)replace the value of x, from equation(1) into equation(2)
[tex]\begin{gathered} x=4y\text{ Equation(1)} \\ x+10y=43\text{ Equation (2)} \\ \text{replacing} \\ 4y+10y=43 \\ 40 \end{gathered}[/tex]