In $5y - 10 = 20$, notice that $5$ multiplies $y$ and that both $-10$ and $20$ are multiples of $5$. What operation with $5$ could you apply to every term to simplify the equation?

You can solve the original equation for $y$, then solve each answer choice for $y$. The equation that gives the same value of $y$ as the original is the equivalent one.

In Desmos, treat $y$ as $x$ (the letter does not matter). Enter the expression f(x) = 5x - 10 - 20. The solutions to $5x - 10 = 20$ are the $x$-values where this graph crosses the $x$-axis (where $f(x) = 0$).

Tap the point where the graph of $f(x)$ crosses the $x$-axis. Note the $x$-value of this intercept; that is the solution of the original equation.

For each answer option, create a similar function by moving everything to one side. For example, for an equation of the form “(left side) = (right side)”, enter g(x) = (left side) - (right side). Check the $x$-intercept of each new graph. The equation whose function has the same $x$-intercept as $f(x)$ is the equivalent equation.

Two equations are equivalent if they have exactly the same solution(s) for the variable. That means any value of $y$ that makes the original equation true must also make the new equation true, and vice versa.

Start with the given equation:

Divide every term on both sides by $5$:

This new equation has the same solutions as the original because we applied the same operation (divide by $5$) to both sides.

From the simplification, the equation equivalent to $5y - 10 = 20$ is $y - 2 = 4$, which matches answer choice B.