#1 is x+1
If x+3 is an even integer, say, for example, 4, then x would have to be an odd integer (x would have to be 1 in the example).
#2 is 5p
If the mangoes are still sold for 5 cents per mango, then the cost would still be 5p.
#3 is 20m, assuming Sam is running at the same rate every minute.
If Sam runs m miles per minute, how many miles will he run in 20 minutes?
A simple proportion can be formed:
m:1 = x:20
Multiply the left side by 20 to get: 20m:20 = x:20
Therefore, x is 20m.