Here is the technique:
1. Cube the first and last term.
2. Square the first term, combine with the second term, and multiply it by 3.
3. Square the second term, combine with the first term, and multiply it by 3.
4. Arrange it.
Answers for your given:
1. (5r + 4p)³ = 125r³ + 300r²p + 240rp² + 64p³
2. (10r+4p)³ = 1000r³ + 1200r²p + 480rp² + 64p³