Here I would use a system of equations. Write out what you know.
Let's use x as the smaller angle and y as the larger one.
x+28=y
x+y=90
We can rearrange the first equation like this
x-y=-28
Now we can add the two equations to get this
2x=62
Divide both sides by two
x=31 degrees
That means the other angle must be 59 degrees.
Is this the answer we're looking for? 59-31=28 if I am correct in my subtraction.
So we get the answers 31 and 59 by using systems of equations.
I hope I helped
