Something has mass of 490 kg and volume of 350 L will it float in water that has density of 1.0 g/mL

This is an awfully simple concept, and basic to everything else in chemistry, physics, and all of reality. You need to read the section again, and keep rereading it until this seems obvious. You have to be pretty sharp in this subject to do the work at all.

When you put an object in a fluid, either gas or liquid, it displaces an amount of fluid equal to its volume. If that volume of fluid weighs more than the object, the object floats. If the fluid weighs less than the object, the object sinks.

The ratio of mass to volume is called density. Water at 4.0C has a density of 1 gram per milliliter. Water warmer than 4.0 is denser than water colder than 4.0, so a lake turns over when the temperature drops, and turns over again in the spring when the temperature rises. That action distributes oxygen to the bottom of the lake to support fish during winter, and the stirs up food to support insects in spring. Without that effect, lakes would all be frozen and lifeless.

Your example has density = 490 kg/350L = 1.4 kg/L = 1.4 g/ml so the object sinks. (Notice that we use either upper case L or lower case l for liter, according to convenience.)