The sum of two numbers is 90.  The second is 10 more than 4 times the first.  What are the two numbers.  

Let one of the numbers be x and the other y.

The sum of two numbers is 90      -------         x + y = 90

The second is 10 more than 4 times the first ----------      y = 4x + 10

We now have a pair of simultaneous equations

x + y = 90....(1)
y = 4x + 10...(2)

Substitute (2) into (1)

x + (4x + 10) = 90

5x + 10 = 90

5x = 80

x = 16

y = 4x + 10 = 4 x 16 + 10 = 64 + 10 = 74

Hence, our two numbers are 16 and 74.