Whenever you have __% more of something and want to find the new value, first convert the percent to a decimal. Then multiply the original value by (1.00+that decimal).
You have 6480 kg of sugar. 75%=0.75. If you want 75% more sugar, you would want 6480*(1.00+0.75) = 6480*(1.75) = 11,340 kg of sugar.