1% of 33 is .33

.33 × 7 =

.3 x 7 = 2.1

.03 x 7 = .21

21 + 2.1 = 2.31

So

7% of 33 = 2.31

You could also do

33% of 7

10% of 7 is .7

1% of 7 is .07

So 11% is .77

.77 × 3 =

.7 × 3 = 2.1

.07 × 3 = .21

2.1 + .21 = 2.31