#color(magenta)("Subtract 10 on both sides of the equation:"#
#2m^(2)+cancel10=210#
#color(white)(aaaa) cancel-10 -10#
On the left side you should be left with 2m^(2), and on the right side you are left with 200:
#2m^(2)= 200#
Next, divide both sides both 2 in order to get the variable and constant on opposite sides of the equals sign. This will allow you to solve for #m# in the next few steps:
#(cancel2m^(2))/cancel2= 200/2#
The 2's cancel out, leaving you with #m^(2)# equal to 100
#m^(2) = 100#
In order to get rid of #m^(2)# to solve for just #m#, you will need to take the square root on both sides of the equation, since the square root is the inverse of a number that's squared:
#sqrtm^(2) = sqrt100#
After you square both sides, you are left with #m# on the left and 10 on the right.
Thus,
#color(purple)("m = 10#