Question 455280
First, define your variables.
x=first number
y=second number
Now write algebraic equations.
Two numbers have a sum of twenty, or x+y=20
The second is five less than four times the first
is  =
five less than  -5
four times  x4
y=4x-5
Now you have a system of equations to solve.  Since the second equation has y isolated, it is simple to use the substitution method.
Substitute y=4x-5 for y in the first equation, x+y=20
x+(4x-5)=20
5x-5=20  Collect like terms
5x=25  Add 5 to both sides
x=5  Divide both sides by 5
To solve for y, substitute x=5 into any of the two equations and solve for y.
y=4x-5
y=4(5)-5
y=20-5
y=15
So the two numbers are 5 and 15 :)