21 less than a number, multiplied by 4, results in 108.find the value of the unknown number.

Mat bought a phone for $100. he has to pay $30 per mouth. if he has paid $640 in total, how many mouth has he had the phone?

50 points and will mark brainlest if you were constructing a triangular frame, and you had wood in the length of 4inches, 4 inches, and 7 inches, would it make a triangle? would you be able to create a frame from these pieces of wood? yes or no? = explain your mathematical thinking:

The deepest part of the swimming pool is 12 feet deep.the shallowest part of the pool is 3 feet deep.what is the ratio of the deeply of the deepest part of the pool to depth of the shallowest part of a pool?