I need help with this question with explanation

The sum of 5consecutive even numbers is 100. what is the first number in this sequence?

Determine the area of a triangle with (see picture below)

At a pizza shop 70% of the customers order a pizza 25% of the customers order a salad and 15% of the customers order both a pizza and a salad if s customer is chosen at random what is the probability that he or she orders either a pizza or a salad