How do you write 25.4 mm in scientific notation

Dylan and dusty plan to take weekly surfing lessons together. if the 2-hour lessons are $20 per person and they plan to spend $100 each on new surfboards, what is the maximum number of lessons the two can take if the total amount spent for lessons and surfboards is at most $480?

Evaluate the expression for the given value of the variable. 5×(h+3) for h=7

Ineed to know the answer to this algebra question.