Find the value of $8.9-79\div10$8.9−79÷10, giving your answer as a decimal.

Find the value of $45\div5-3.2$45÷5−3.2, giving your answer as a decimal.

Find the value of $4.2+28\div10$4.2+28÷10, giving your answer as a decimal.

Find the value of $0.38+12\div100$0.38+12÷100, giving your answer as a decimal.