7+2x9-1/2

7 + 2 x 9 - 1/2
= 7 + 18 - 1/2
=  7 x 2 / 1 x 2 + 18 x 2 / 1 x 2 - 1/2
= 14/2 + 36/2 - 1/2
= 50/2 - 1/2
= 49/2