Question 262227
First, draw a venn diagram with 2 circles. draw lines in each oval area and a line outside on the right side. These four lines need four numbers. 
--
step 1 - place "A" on the first line, "x" on the second line, "B" on the third line and "3" on the outside fourth line.
---
step 2 - now we have some equations
(i) A + x + B + 3 = 15
(ii) A + x= 7
(iii) B + x = 8
adding (ii) and (iii), we get
(iv) A + B + 2x = 15
substituting (i) and (iv) we get
A + x + B + 3 = A + B + 2x
subtracting A and B we get
x + 3 = 2x
subtract x to get
x = 3.
3 studied both Latin and Greek