Fast the area of a triangle that is similar to the one below is 1/9 the area of this triangle. what is the length of the base of the similar triangle?

height = 10 ft
base = 21 ft

Similar so they are in proportion

find area first
area=1/2bh
area=1/2(21)(10)
area=105 square feet
1/9 of that
11 and 2/3

1/2 times b times h=11 and 2/3
times 2
b times h=23 and 1/3
21/x times 10/x=23 and 1/3
210/x^2=70/3
times x^2 both sides
210=70x^2/3
times 3/70 both sides
9=x^2
sqrt both sides
3=x

the scale factor is 1/3

so
the base is 21/3 or 7ft