are my chemistry calculations right?

Question

density=mass/volume

d=612/245=2.497959.....

d=68/6.48=10.493827.......

Answer 1

The math is fine.

However, there is no mention as to units, which are VERY important when doing calculations.

If the 612 is a volume, such as mL, then no, the fraction should be inverted.

Likewise, there is no regard for significant figures in your calculations. The answer to the first one should be rounded to 2.50 (3 sig figs), and the bottom one to 10.
or 1.0 x 10^1 (2 sig figs)

Answer 2

remember your units and sig-figs are important also.