Solve the system by substitution
-4.5x-2y=-12.5
3.25x-y=-0.75

Assuming you mean > -4.5x - 2y = -12.5; 3.25x - y = -0.75 as a system of equations we shall solve.
So solve 3.25x − y = −0.75 for y
3.25x − y + −3.25x = −0.75 + −3.25x (Note we are adding -3.25x to both sides)
−y = −3.25x − 0.75
Now divide both sides by -1.

Now we must substitute 3.25x + 0.75 for y in −4.5x − 2y = −12.5
-4.5x - 2y = -12.5
-4.5x - 2(3.25x + 0.75) = -12.5
Now simplify both sides.
-11x - 1.5 = -12.5
Then add 1.5 to both sides.
-11x - 1.5 + 1.5 = -12.5 + 1.5
-11x = -11
Then divide both sides by -11.

Now we need to substitute 1 for x in y = 3.25x + 0.75.
y = 3.25x + 0.75y = (3.25)(1) + 0.75
When we simplify both sides we get y = 4
So we get x = 1 and y = 4. Hope this helps!