Add 0.2x to both sides
1.2x+0.7= 1
1.2x=.3
x=.3/1.2
x=.25
option #2
subtract .7 on both sides
x=1-.7-.2x
x=.3-.2x
1.2x=.3
x=.25
423%. Calculate this with
The probability the first marble will be blue is 28/40
The probability the second marble will be red is 12/39
The reason is because 28 + 12 = 40, so this makes the denominator for our first outcome, but then a marble is removed making our denominator 39 because 40-1 = 39.