It was long since I (visit) my brother last. (Use the right form of verb)

His grandmother looked after him. (Make it passive) = He was looked after by his grandmother.

Five miles is a long distance. (Note: Distance, money, and time are usually treated as singular units.)

I cut the mango by a knife. = I cut the mango with a knife.

Affect (Verb): The heavy rain will affect the crop production this year.

Effect (Noun): The medicine had a positive effect on his health.

The police is investigating the matter. = The police are investigating the matter.

I, and not my friends, are to blame. = I, and not my friends, am to blame.