I need help with this question but keep f getting decimals, it's not supposed to be a decimal for the answer. were solving systems by substitution

here's the question and will give brainy to someone who solves both

4x - 7y = 10
y = x - 7

x = 16 - 4y
3x + 4y = 8

Christine wong has asked dave and mike to her move into a new apartment on sunday morning. she has asked them both, in case one of them does not show up. from past experience, christine knows that there is a 40% chance that dave will not show up and a 30% chance that mik a. what is the probability that both dave and mike will show up? (round your answer to 2 decimal places.) b. what is the probability that at least one of them will show up? c. what is the probability that neither dave nor mike will show up? (round your answer to 2 decimal places.)e will not show up. dave and mike do not know each other and their decisions can be assumed to be independent.