Answer:
D2=21/24 mile
Step-by-step explanation:
Her it is not specified if it is base or height, it only talks about dimensions, so let's work with dimensions
A=1/12
D1=4/21mile, D2=?
Area of a triangle
A=((D1*D2)/2) → 2A=D1*D2 → D2=2A/D1 so D2=(2*1/12)/(4/21) =(1/6)/(4/21) = (1*21)/(6*4)=21/24 mile
