`a)87+106+13-42:7`
`=87+106+13-6`
`=193+13-6`
`=206-6`
`=200`
`b)15.2^3+7.4^2-3^5:3^2`
`=15.8+7.16-3^3`
`=120+112-27`
`=205`
`c)2.[(6^2-24):4]+2021`
`=2.[(36-24):4]+2021`
`=2.[12:4]+2021`
`=2.3+2021`
`=2027`
`d)7^2.10:{500:[10^2-(5^2. 3-25.2021^0)]}`
`=49.10:{500:[100-(25.3-25.1)]}`
`=49.10:{500:[100-50]}`
`=49.10:{500:50}`
`=49.10:10`
`=49`