The area of a triangle is 10 cm were the power to it’s bases 3 cm less than twice its height what is the height of the triangle

Really need on these. i have no idea what to do

Jack did 3/5 of all problems on his weekend homework before sunday. on sunday he solved 1/3 of what was left and the last 4 problems. how many problems were assigned for the weekend?

An airplane travels at an unknown elevation before it descends 3 miles to an elevation of 15 miles. find the elevation of the plane before its descen.