Answer:
Definition: U-shaped valleys form through glacial erosion. Glaciation develops in established v-shaped river valleys where the ice erodes the surrounding rocks to create a “U” shaped valley with a flat bottom and steep sides. Glacier movement is driven by gravity
Well to find this out you need to make an equation
s+7=j
So for example if Johnny's sister is 15 then Johnny would be 22 because
s(sister's age) +7(number of years difference between their ages)=22(Johnny's age)
