1 cent can be added by adding a 7-cent stamp and taking away two 3-cent stamps. 2 cents can be added by adding three 3-cent stamps and taking away one 7-cent stamp. Hence any value more than 7 +2(3) = 13 cents can always be accommodated.
1 : you would use a graduated cylinder . 2 : , you would use a yard stick or maybe a ruler if you are not able to find one. You can also use a meter stick.