Dear Deeksha, I am from a science background so I am able to solve it. Let do it

The density of the solution is 3.12 g/ml (you forget mention unit)

A volume of solution is 1.5 ml

Mass of the solution = volume * density

= 1.5*3.12

4.68 g  ~ 4.7 (2 significant figure).

I hope I cleared your doubt.

All the best dear Deeksha.