Please help it for math

Rearrange the formula c^2 = a^2 + b^2 for b

Give the equations of two different lines that are perpendicular to the line 3x + 4y = 7.

Which questions would most a reader identify the author's purpose for writing? check all that apply. what type of text is this? what type of reviews did the book receive? how many copies of the book have been sold? what is the central idea? how does this text make one feel?