The sum of two numbers is 58 the larger number is three more than four times the smaller number find the two numbers

X+Y=56
X=Y-16
(Y-16)+Y=56
2Y=56+16
2Y=72

Y=72/2
Y=36 ANS.
X+36=56
X=56-36
X=20 ANS.Let x = big number 
Let (56 - x) = small number 
The smaller number (56 - x) is 16 less than the larger number x. 
This is written as (56 - x) = x - 16. 
We now simply solve for x. 
Once we find x, we then can find the two numbers. 
56 - x = x - 16 

56 + 16 = x + x 

72 = 2x 
72/2 = x 
36 = x 
The big number is 36. 
The smaller number is 56 - 36 or 20.