The smallest of three consecutive integers is added to the largest, the result so obtained is 15 less than 4 times the middle integer. Find the integer.

smallest --- x

middle --- x+1
largest --- x+2

"smallest is added to the largest" ---> x+2 + x =2x+2
4 times the middle = 4(x+1) = 4x+4

2x+2 +15 = 4x+4
-2x = -13
x = 13/2
but x has to be an integer, so there is no solution to your problem

(notice that my solution does work if we let the 3 numbers be 6.5, 7.5, and 8.5
check:
add the first to the last: 6.5+8.5 = 15
4 times the middle: 4(7.5) = 30
is 15 less than 30 by 15 ? , YES )