Answer: The approximate percent increase is 121.42857%. This is a rounded value. To get this, first you would need to find out which increased and in what direction. Of course, the 70 turned into an 85. So you can divide 85 by 70 and receive a number. Then in whatever form you found it, decimal, fraction, or even percent straight away, ensure the value is a percentage.
70 -> 85
85/70
About 1.21 [decimal]
1.21 x 100 = 121 [add the %]
121% [rounded]