Answer is 38.38 g
Explanation;
To find out the mass, we can apply the simple formula,
d = m / v
Where, d is the density of the substance, m is the mass and v is the volume of the substance.
Values of d and v are given as follows;
d = 1.23 g/mL
v = 31.2 mL
m = ?
By applying the formula,
1.23 g/mL = m / 31.2 mL
m = 1.23 g/mL x 31.2 mL
m = 38.376 g = 38.38 g