Question

how to solve :
x+y=10
25x+50y=.40(10)

Answer 1

Solve for a variable. Lets use the first statement.
x+y=10
x=10-y

Now, use this understanding of what "x equals" and apply it to the second statement.
x=10-y, therefore
25(10-y)+50y=4
250-25y+50y=4
250+25y=4
25y=-246
y=61.5
Use this numerical value of y in the simplest statement to solve for the other numerical value of x.
x+61.5=10
x=(10-61.5)

This system is solved for x=(10-61.5) and y=61.5