To develop a product that warms peoples hands would you use an exothermic or endothermic reaction? why?

Exothermic because exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings, so if you want to warms people's hands you should use exothermic chemical reaction for the product.

It will take annabelle 4 hours to complete her homework. if it took her 3 hours to finish 75%, then it probably took her 1 hour for every 25% she finished. if she finished 75%, she has 25% left to be done or 100% complete. 25% = 1 hour. so 3 hours + 1 hour = 4 hours or 100% complete