Answer A. is correct I’m pretty sure
I'll go out on a limb and suppose you're given the matrix

and you're asked to find the determinant of

, where

and given that

.
There are two properties of the determinant that come into play here:
(1) Whenever a single row/column is scaled by a constant

, then the determinant of the matrix is scaled by that same constant;
(2) Adding/subtracting rows does not change the value of the determinant.
Taken together, we have that
Answer:
Step-by-step explanation:
Scale= length on drawing / actual length
Let the actual length b x
3:10=2/5/x
3/10=2/5x
Cross multiply
15x=20
x=4/3
The actual length is 4/3
Answer:
The width of the river is about 8.39 m.
Step-by-step explanation:
Tan = Opposite/Adjacent
The width of the river is the side of a right triangle opposite the angle of 40°. The 10 m distance is the length of the side adjacent to the measured angle. So, we have ...
tan(40°) = width/(10 m)
Multiplying by 10 m, we get ...
width = (10 m)tan(40°) ≈ 8.39 m
The width of the river is about 8.39 m.