Bob switches cell phone plans from verizon to tmobile. the monthly cost of his new plan is half the cost of his old plan, plus he added the iphone 6s to his new plan which costs an additional $27.50 per month. if bob's new monthly bill with tmobile is $70 total(plan and phone), then how much is he saving per month by switching from verizon to tmobile? (analyze, equation, solve, check and interpret, conclusion)