PLEASE HELP!!

ABCD is a rectangle. If AC = 4x - 60 and BD = 30 - x, find BD.

Write an expression that has three terms and simplifies to 4x - 7. identify the coefficient(s) and constant(s) in your expression

Awater holding tank measures 105 m long, 50 m wide, and 8 m deep. traces of mercury have been found in the tank, with a concen- tration of 60 mg/l. what is the total mass of mercury in the tank? answer in units of kg.

With alll of except for the 2 that i did already