Final answer:
The entire right side of the mathematical sentence that Robert wrote would be erased, which includes the distributive property application of 7 x (30 + 7), leading to the erased result of 259.
Step-by-step explanation:
Robert's little sister erased the entire right side of the mathematical sentence after the equal sign. This would include all calculations and results that were supposed to follow. Since Robert started with 7 x (30 + 7) =, he was demonstrating the use of the distributive property, which means he would have calculated 7 x 30 + 7 x 7, which simplifies to 210 + 49. Therefore, the entire right side of the equation that was erased should be 210 + 49, which equals 259.
It's important to eliminate terms wherever possible to simplify the algebra and then check the answer to see if it is reasonable, which in this case, it is.