I have like a few really basic but idontknow how to solve questions. hope someone can help! thanks in advance! ^^

1) Sini was 12years oldr than Sana 4 years ago

He will be twice as old as sana in 4 years time

Find the sum of their ages 3 years ago

2) The length of a rectangle is increased by 16% and its width is decreased by 16%. Find the percentage increase or decrease in the area.

3) During a cross-country race, Newson ran 50% of the journey at 10km/h, the next 35% at 7km/h and remaning journey at 5km/h. Calculate the average speed in km/h of Newson for the whole journey

Thankssss!