1. **State the problem:** We need to find the mass of chemical B when 2.2 g of chemical A is used, given a linear relationship between the masses. 2. **Identify the relationship:** The graph is a straight line through the origin, so the relationship between mass of B ($y$) and mass of A ($x$) is linear and can be written as: $$y = kx$$ where $k$ is the constant of proportionality. 3. **Find the constant $k$:** From the graph, when $x = 4$ g, $y = 2.8$ g. $$k = \frac{y}{x} = \frac{2.8}{4} = 0.7$$ 4. **Calculate mass of B for 2.2 g of A:** $$y = 0.7 \times 2.2 = 1.54$$ g 5. **Answer:** When 2.2 g of chemical A is used, 1.54 g of chemical B is needed.