what is 12m-28=34

You can start by isolating m.

To isolate m, take away -28, or add 28 to both sides:

12m - 28 + 28 = 34 + 28

12m = 62

Now isolate m further by dividing each side by 12:

12m/12 = 62/12

m = $${\frac{{\mathtt{62}}}{{\mathtt{12}}}} = {\frac{{\mathtt{31}}}{{\mathtt{6}}}} = {\mathtt{5.166\: \!666\: \!666\: \!666\: \!666\: \!7}}$$ or $${\mathtt{5}}$$ $${\frac{{\mathtt{1}}}{{\mathtt{6}}}}$$