He has not read 152 pages.
If y is the number of pages he has not read and x is the number of pages he has read, then:
x+y=193
x=1/4y+3 (the number of pages he has read is three pages more than one fourth the number of pages he hasn't read)
Since we have two equations, solving for one variable will allow us to substitute that value into the other equation. Since x is already isolated in the second equation, we will use that, substituting the value of x from the second equation into the first.
(1/4y+3)+y=193
5/4y+3=193
5/4y=190
y=152
