1. **Problem statement:** Find the value of each expression for given values of variables. 2. **Formula and rules:** Substitute the given values into the expressions and perform arithmetic operations following order of operations (PEMDAS/BODMAS). 3. **Part 1a:** Given $x=3$, $y=5$, expression: $x - 2y$ Substitute: $3 - 2 \times 5$ Calculate multiplication: $3 - 10$ Calculate subtraction: $-7$ 4. **Part 1b:** Expression: $x^3 + xy$ Substitute: $3^3 + 3 \times 5$ Calculate powers and multiplication: $27 + 15$ Calculate addition: $42$ 5. **Part 1c:** Expression: $y^2 - \frac{10x}{y}$ Substitute: $5^2 - \frac{10 \times 3}{5}$ Calculate powers and multiplication: $25 - \frac{30}{5}$ Calculate division: $25 - 6$ Calculate subtraction: $19$ **Final answers for Exercise 2.1 part 1:** a) $-7$ b) $42$ c) $19$