To make a 140 g bar last, storage matters more than most people expect. A solid soap that sits in water softens on the surface and dissolves much faster, so the main rule is to keep it dry between uses. Place it on a soap dish with drainage holes or a ribbed holder so water can run off and air can reach the bottom. A wet bar left in a shallow puddle will form a sticky layer that gets wasted the next time you pick it up.
In the bathroom, choose a spot that is not directly under the shower spray. In the kitchen, keep it away from the edge of the sink where water splashes. If you travel with the bar, pack it in a breathable container such as a soap tin with holes, or wrap it in a washcloth and let it dry out after the journey. The bar does not need refrigeration – ordinary room temperature is fine.
There is no fixed lifetime for a bar of soap because it depends on how often it is used, how many people use it, and how hard your water is. You can slow down consumption by rotating it with another soap, and if you prefer a smaller piece that is easier to hold and dries faster, you can cut the bar in half with a clean knife before first use.