As given by the question
There are given that the sum of the two numbers is at least 8.
Now,
Let the unknown numbers be x and y
Then,
If the sum of the two numbers is at least 8 then:

Similarly, the sum of one of the numbers and 3 times the second number is no more than 15
Then,

Now,
From the both of the inequality:

Then, find the first and second nuber:
So,

Then, Put the value of x into the second equation
Then,

Then,
Put the value of y into the equation (a)

Hence, the first number and second number is shown in below:

The graph of the given result is shown below: