Answer:
12
Step-by-step explanation:
area of a trapezoid :
[tex]A = \frac{a+b}{2} h[/tex]
where a and b = length of bases and h = height
here, we are given the area, the length of one base and the height
we want to find the other base length
we can do this by plugging in what we are given and then solving for the unknown variable
first lets define our known variables
Area (A) = 42 , height (h) = 4 and length of one of the bases (a) = 9
we then plug this into the formula and solve for b, the other base length
recall formula : [tex]A = \frac{a+b}{2} h[/tex]
A = 42 , h = 4 , a = 9
[tex]42 = \frac{9+b}{2} 4[/tex]
now solve for b
divide both sides by 4
[tex]10.5=\frac{9+b}{2}[/tex]
multiply both sides by 2
21 = 9 + b
subtract 9 from both sides
12 = b
the other base length is 12
