First we need to convert them into like terms. Three fifths is twelve twentieths. Three fourths is fifteen twentieths. Together that is twenty-seven twentieths. That is one and seven twentieths or 1.35 in decimal.

One half is five tenths. Add three tenths, gives eight tenths. Simplify that by dividing the two values by their highest common factor, which is 2. That gives you four fifths.