Q3. ANSWER
From the first and third rows and the third and fourth columns we get:
                    a + 2b + c  = 32 ----------- I
                    a + 2b + d  = 30 ----------- II
                    2a + 2c      = 31 ----------- III
                    2b + 2d      = 31 ----------- IV
 
From equation III, we get                                            a + c = 15.5
Substitute this in I equation gives                                  b = 8.25
Putting the value of b in equation IV gives                      d = 7.25
Substituting these values of b and d in equation II gives     a = 6.25
Putting the value of a in equation III gives                      c = 9.25
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