Let's solve the problem step by step:

Part (a) Identifying the Equations:

An equation is a mathematical statement that contains an equals sign (=), indicating that two expressions are equal.

From the options provided:

1. $d = 3d - 19$ → This is an equation (contains an "=" sign). ✅
2. $16d$ → This is not an equation (no "=" sign). ❌
3. $d = 14$ → This is an equation (contains an "=" sign). ✅
4. $70 - 18d$ → This is not an equation (no "=" sign). ❌
5. $4d + 15$ → This is not an equation (no "=" sign). ❌
6. $25 = d$ → This is an equation (contains an "=" sign). ✅

Answer: The three equations are: $d = 3d - 19$, $d = 14$, and $25 = d$.

Part (b) Difference Between an Equation and an Expression:

• An equation is a mathematical statement that shows equality between two expressions, containing an equals sign (=).
• An expression is a mathematical phrase made up of variables, constants, and operations, but it does not include an equals sign.

Would you like further clarification or a breakdown of any part? Let me know!

Related Questions:

1. What steps would you follow to solve the equation $d = 3d - 19$?
2. How do you convert an expression like $4d + 15$ into an equation?
3. What are some real-life examples of equations and expressions?
4. What does it mean to "simplify" an expression like $16d$?
5. How can we verify that a solution satisfies an equation?

Tip:

When distinguishing between an equation and an expression, look for the equals sign! If there isn’t one, it’s an expression.