Savanna had 40 iris blooms last year. this year, she had 15% more iris blooms. how many more iris blooms did savanna have this year?

Lets begin with an example.

You have 100 apples. 40 % of your apples are 40. Sounds complicated?

Here is the calculation in words, number of apples times 40 percentage.

By equation: 100 * 40/100= 40. Simple huh?

% symbol represents 100. 
% 15 equals 15/100; 20% is equal to 20/100 or 1/5 in a simplified way.

Have a look to question. 40 iris at last year, 15 % MORE iris this year.

What is the 15 % of 40 iris? That's the question at the end.

Recall apple example at the beginning.

40 iris * 15/100 = 6.

So, there are 6 MORE iris blooms this year. This year Savanna has totally 46 iris.