Albert says these two systems are similar
#1
8x+9y=48 12x+5y=21
#2
8x+9y=48. -8.5y=-51
are they similar?

we solve the second system: (it is more easy).
8x+9y=48
-8.5y=-51    ⇒y=-51/-8.5=6

8x+9(6)=48
8x+54=48
8x+54-54=48-54
8x=-6
x=-6/8=-3/4

Then; in te second system the solution is : x=-3/4; y =6

Now, we replace "x" by "-3/4" and "y" by "6", in the first systmen.

8x+9y=48
8(-3/4)+9(6)=-6+54=48. verified

12x+5y=21
12(-3/4)+5(6)=-9+30=21    verified

Therefore,
These two wystems are similar.