Solution:
a=-2 b=1 c=4 d=0
Analysis:
When we multiply a matrix by a constant, we multiply each term of the matrix by the constant.
In this case, as we need to find the value of the initial matrix, we can divide each term of the matrix by the constant. In this case, let´s divide by -5
So, it would be:
a=10/-5 a=-2
b=-5/-5 b=1
c=-20/-5 c=4
d=0/-5 d=0