If you add the two equations, one of the grouped terms cancels out. If you subtract one equation from the other, the other grouped term cancels out. This will give you two simpler linear equations in $x$ and $y$.

Once you have the simpler system, solve it in a way that gets you $y$ efficiently (for example, express $x$ in terms of $y$ from one equation and substitute into the other), and then multiply that $y$ value by 28.

In Desmos, enter the first equation exactly as given: (4x + 3y) - 2(x - y) = 11. Then enter the second equation: (4x + 3y) + 2(x - y) = 83. Desmos will plot both lines.

Use the cursor (or tap) to click on the point where the two lines intersect. Desmos will display the coordinates of this intersection as $(x, y)$; note the y-coordinate.

In a new expression line, type 28* followed by the y-coordinate of the intersection point (for example, 28*(-25/7) if that is the y-value you saw). The value that Desmos outputs for this expression is the value of $28y$.

Notice that both equations use the same pieces, $(4x + 3y)$ and $2(x - y)$, but with opposite signs.

Add the two equations so that $-2(x - y)$ and $+2(x - y)$ cancel:

This simplifies to:

Divide both sides by 2:

Now subtract the first original equation from the second to eliminate $(4x + 3y)$:

This simplifies to:

Divide both sides by 4:

So the original system is equivalent to the simpler system $4x + 3y = 47$ and $x - y = 18$.

From $x - y = 18$, solve for $x$ in terms of $y$:

Substitute this expression for $x$ into $4x + 3y = 47$:

Distribute and combine like terms:

Subtract 72 from both sides:

Divide both sides by 7:

Now use the value of $y$ to find $28y$:

Simplify by dividing 28 by 7:

So the value of $28y$ is $-100$.