You can do simple arithmetic with percentages in Soulver:
120 + 10% | 132500k - 30% | 350k
Soulver also includes a set of percentage phrases for all scenarios you're likely to run into.
10% of 200 | 2020 is what % of 200 | 10%20 is 10% of what | 200
10% off 200 | 180180 is what % off 200 | 10%180 is 10% off what | 200
10% on 200 | 220220 is what % on 200 | 10%220 is 10% on what | 200