A tub of water is filled with an Initial (starting) volume of 100 L. A toy is placed in the tub and the water level rises to 115 L. The toy has a mass of 15 kilograms. What is the density of the toy in Kg/L?

I was told it was 1, can someone please explain why that is?

Neurons are components of the nervous system of the body that transmit signals as electrical impulses travel along their length. these impulses propagate when charge suddenly rushes into and then out of a part of the neutron called an axon. measurements have shown that, during the inflow part of this cycle approximately 5.6x10^11 na per meter, each with a charge of e enter the axon. how many coulombs of charge enter a 1.10 cm length of axon during this process