18. 0.796 + 13 = 13.796 (the 13 is a whole number, so just put it in front of the decimal)
19. 15.63 + 24.36 = 39.99 (1+2=3 ; 5+4=9 ; 6+3=9 ; 3+6=9)
20. 19.86 - 4.94 = 14.92
21. 82 - 67.18 = 15.18 (again, whole number, there's no decimals to subtract, so leave them be)
22. 14.39 - 12.16 = 2.23 (1-1=0 ; 4-2=2 ; 3-1=2 ; 9-6=3)