Material A has Y = 1.5 × 10¹¹ Pa and breaks at 3.0 × 10⁸ Pa…

Step 1. (a) A: $\dfrac{1.5 \times 10^{8}\ \text{Pa}}{1.5 \times 10^{11}\ \text{Pa}} = 1.0 \times 10^{-3}$. B: $\dfrac{1.5 \times 10^{8}\ \text{Pa}}{7.5 \times 10^{10}\ \text{Pa}} = 2.0 \times 10^{-3}$.

Step 2. (b) A: $\dfrac{3.0 \times 10^{8}\ \text{Pa}}{1.5 \times 10^{11}\ \text{Pa}} = 2.0 \times 10^{-3}$. B: $\dfrac{4.5 \times 10^{8}\ \text{Pa}}{7.5 \times 10^{10}\ \text{Pa}} = 6.0 \times 10^{-3}$.