We can model the problem as a linear equation of the form:
[tex]y=mx+b[/tex]Where:
m = Slope (Rate of change)
b = y-intercept (Initial value)
a)
Since it is descending at a rate of 25ft per minute, the slope is:
[tex]m=-25[/tex]So, the equation is:
[tex]y=-25x+b[/tex]b) We know that the ballon was 425ft above the ground 21 minutes after it began its descent, so:
[tex]\begin{gathered} y=425,x=21 \\ so\colon \\ 425=-25(21)+b \\ 425=-525+b \\ b=950 \end{gathered}[/tex]Therefore, the balloon was 950ft when it began its descent, so, we can conclude that the y-intercept is 950, now the equation is complete
[tex]y=-25x+950[/tex]c) We need to know for which value of x, y is equal to 0, so:
[tex]\begin{gathered} y=0 \\ 0=-25x+950 \end{gathered}[/tex]Solve for x:
[tex]\begin{gathered} 25x=950 \\ x=\frac{950}{25} \\ x=38 \end{gathered}[/tex]The balloon will land after 38 minutes
