$myVar='myVar is plus5 which is '.$myNumber.'+5
myVar is plus10 which is '.$myNumber.'+10
myVar is plus20 which is '.$myNumber.'+20';
I have a number variable "$myNumber" which is like the above.

I like to replace the text plus5 to 105, the text plus10 to 110 and the text plus20 to 120.

So my target result will be like the following.
target result

$myTarget_result='myVar is 105 which is 100+5
'myVar is 110 which is 100+10
myVar is 120 which is 100+20';
How can I get $myTarget_result from $myVar?