how to solve a 3x3 magic square when some (5) numbers are provided

Question

my 3x3 has some numbers provided but don't know how to figure out the missing numbers:

 

_     5     _

33    _    49

_     77   19

 

Any help is appreciated

Answer 1

Call the missing numbers A, B, C, D from left to right, top to bottom.

A+5+B=33+C+49=D+77+19=A+33+D=5+C+77=B+49+19=A+C+19=B+C+D.

A+B+5=C+82=D+96=A+D+33=B+68=A+C+19=B+C+D.

D+96=A+D+33, 96=A+33, A=63. Replace A in other expressions and rewrite the list, omitting duplicates:

B+68=C+82=D+96=B+C+D. C+D=68 and C-D=14, so, adding, 2C=82, C=41. So, D=27.

B+68=41+82, so B=55. The common sum is 123.

63	5	55
33	41	49
27	77	19