Let x be the smaller number and y the larger:
As the numbers are consecutive y - x = 1
And 3y + x = 31 (3 times the large added to the smaller)
From the first equation y = x + 1
By substituting:
3(x + 1) + x = 31
3x + 3 + x = 31
4x = 28
x = 7
y = x + 1
y = 7 + 1 = 8
