What is ##y+10## when ##y=43##?

##43+10= 53##

There are two pieces of information given.
##y+10## tells us what operation is being done with ##y##.
y will be increased by 10.
The other piece of information is giving a value for ##y##
##y=43##
Replace the y in ##(color(red)(y) +10)## by the value ##color(red)(43)##
##color(red)(43) +10 = 53##
The answer would be different for every different value of y.