Can y’all helpmeet please?

Me find the missing dimension of a triangle height: 7 in., area: 21^2

The multiplication property of zero states that the product of any number and 0 is 0. what must be true about either a or b to make ab=0

The marked price of an article is 25% above its selling price and the cost price is 30% less than its marked price . find the discount percent and gain percent. only a brainlest can solve it i will mark you brainlest