venue rent: $7000$

advertising cost: $1000$

service staff cost: $2000$

equipment for each participant: $10$

refreshments for each participant: $15$

they plan to charge $50$ per participant

$1.$ how many participants do they need to break even $($compute by contribution margin method$)?$

$2.$ what is the sales revenue needed to break even $($compute by equation method$)?$