10 cm^3 / 1.2 g = 23cm^3 / x g

So we want to solve for x. We can cross multiply to get:

(10 cm^3) * (x g) = (23 cm^3) (1.2 g)

All of the units cancel, so we are left with:

10 * x = 23 * 1.2

Divide both sides by 10 to get:

x = (23 * 1.2) / 10

x = 2.3 * 1.2

x = 2.76

So there are 2.76 g of hemoglobin in 23 cm^3 of a normal specimen of human blood.