In 2014, Donald's weekly pay was $640. In 2015, Donald's weekly pay was $668,80. Work out the percentage increase in Donald's pay between 2014 and 2015.

To work out the percentage increase, you need to find out the change in his weekly wage between the two years, and divide it by his original pay. You can use the formula (new-old)/old.
His new wage is $668.80, and his old wage was $640. So the change in wage (new-old) = $28.80. You then divide this by the old wage. $28.80 / $640 = 0.045
To turn this into a percentage, you need to multiply it by 100. Hence, the percentage increase in wage equals 4.5%