Answer:
58.6
Step-by-step explanation:
Use the formula 
solving for x (b)
=
≈58.58327
and 58.58327 rounds to 58.6
It helps to imagine the variable a sort of as a unit. Like with 5 minus 12 lemons, it has no bearings on the addition/subtraction here.
Factor out a and subtract.
This basically says all the steps ! If you have any questions just tell me :)
$90 because 200-10=180 and divide 180 by 2 which is 90.