a: =3990-(463*72-39^2):15
=3990-2121=1869
b: =1995-963-172=860
c: =33/11-7/11=26/11
d: =3/2+5=13/2
`@` `\text {Answer}`
`\downarrow`
`a,`
`3990 - (463 \times 72 - 39 \times 39) \div 15`
`= 3990 - (33336 - 1521) \div 15`
`= 3990 - 31815 \div 15`
`= 3990 - 2121`
`= 1869`
`b,`
`1995 - 321 \times 3 - 6020 \div 35`
`= 1995 - 963 - 172`
`= 1032 - 172`
`= 860`
`c,`
`3 - 7/11`
`= 33/11 - 7/11`
`= 26/11`
`d,`
`1/4 \div 1/6 + 5`
`= 1/4 \times 6 + 5`
`= 3/2 + 5`
`= 13/2`