how to apply the lift equation-.-

A plane is traveling at a speed of 100 knots at a certain angle of attack. the lift on it is found to be 2000 kilo-gram.

a)if its angle of attack remains unchanfed but its speed is slowed down to 80 knots, what would be the lift be? (air density and wing area remain unchanged)

b)if the weight of the plane is 1000 kilo-gram, and if the angle of attack remains unchanged, what would the speed be before the starts to sink?

i am not good at maths..can anyone answer me..thank you;(

1600 kilograms is the answer to the first question.....2000 kilograms devided by 100 kts equals 20 kilograms a knot....80 knots times 20 kilograms equals 1600 kilograms
your second question
you produce the same lift as the airplane weighs in level flight.....if everything remained the same from your first question...and you weigh 1000 kilograms the airplane will begin to sink at 49.99 knots......50 knots times 20 kilograms equals 1000 kilograms..anything less and you begin to come down

Actually lift varies by the square of the velocity so at 80 the lift would be 64% of what it was at 100.
Question 2 to support half the weight speed would be 1 over square root of two times the speed approx 70 knots