Answer:
Part 1) The length of the longest side of ∆ABC is 4 units
Part 2) The ratio of the area of ∆ABC to the area of ∆DEF is 
Step-by-step explanation:
Part 1) Find the length of the longest side of ∆ABC
we know that
If two figures are similar, then the ratio of its corresponding sides is proportional and this ratio is called the scale factor
The ratio of its perimeters is equal to the scale factor
Let
z ----> the scale factor
x ----> the length of the longest side of ∆ABC
y ----> the length of the longest side of ∆DEF
so

we have


substitute

solve for x


therefore
The length of the longest side of ∆ABC is 4 units
Part 2) Find the ratio of the area of ∆ABC to the area of ∆DEF
we know that
If two figures are similar, then the ratio of its areas is equal to the scale factor squared
Let
z ----> the scale factor
x ----> the area of ∆ABC
y ----> the area of ∆DEF

we have

so


therefore
The ratio of the area of ∆ABC to the area of ∆DEF is 