Answer:
The answer is y=-15
Explanation:
In order to determine the number, we have to express the problem into an equation. Every time that we want to know a value of a variable, we have to express an equation that it contains the variable.
Let's express every part of the statement:
Three fifths=

A number= y
negative 9= -9
Putting together every part into an equation:

Finally, the value of the number "y" is -15.