how do you find 20% of 6.87

or just 20/100*6.87

$${\frac{{\mathtt{20}}}{{\mathtt{100}}}}{\mathtt{\,\times\,}}{\mathtt{6.87}} = {\frac{{\mathtt{687}}}{{\mathtt{500}}}} = {\mathtt{1.374}}$$

Use a proportion, in this case $${\frac{{\mathtt{x}}}{{\mathtt{6.87}}}} = {\frac{{\mathtt{20}}}{{\mathtt{100}}}} \Rightarrow {\mathtt{x}} = {\frac{{\mathtt{687}}}{{\mathtt{500}}}} \Rightarrow {\mathtt{x}} = {\mathtt{1.374}}$$